INSURED MUNICIPAL SECURITIES TRUST 17TH DIS SER & SER 6
485BPOS, 1994-04-20
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    As filed with the Securities and Exchange Commission on April 20, 1994
        
                                                    Registration No. 33-02389*
                                                                              


                        SECURITIES AND EXCHANGE COMMISSION
                              Washington, D.C. 20549

                          POST-EFFECTIVE AMENDMENT NO. 8
        
                                        To
                                     FORM S-6

                     FOR REGISTRATION UNDER THE SECURITIES ACT
                     OF 1933 OF SECURITIES OF UNIT INVESTMENT
                         TRUSTS REGISTERED ON FORM N-8B-2

    A.   Exact name of trust:

              INSURED MUNICIPAL SECURITIES TRUST, 17TH DISCOUNT SERIES &
              SERIES 6, 18TH DISCOUNT SERIES, 19TH DISCOUNT SERIES & SERIES 7,
              20TH DISCOUNT SERIES and 21ST DISCOUNT SERIES

    B.   Name of depositor:  BEAR, STEARNS & CO. INC.

    C.   Complete address of depositor's principal executive office:

              245 Park Avenue
              New York, NY 10167

    D.   Name and complete address of agent for service: 

              PETER J. DeMARCO              Copy of comments to: 
              Managing Director             MICHAEL R. ROSELLA, ESQ. 
              Bear, Stearns & Co. Inc.      Battle Fowler
              245 Park Avenue               280 Park Avenue
              New York, NY 10167            New York, NY 10017
                                            (212) 856-6858
       
        
    It is proposed that this filing become effective (check appropriate box)
       
    /   /  immediately upon filing pursuant to paragraph (b) of Rule 485
    / x /  on April 29, 1994 pursuant to paragraph (b)
        
    /   /  60 days after filing pursuant to paragraph (a)
    /   /  on (       date       ) pursuant to paragraph (a) of Rule 485



    *    The Prospectus included in this Registration Statement constitutes a
         combined Prospectus as permitted by the Provisions of Rule 429 of the
         General Rules and Regulations under the Securities Act of 1933 (the
         "Act").  Said Prospectus covers units of undivided interest in
         Insured Municipal Securities Trust, 17th Discount Series & Series 6,
         18th Discount Series, 19th Discount Series & Series 7, 20th Discount
         Series and 21st Discount Series, covered by prospectuses heretofore
         filed as part of separate registration statements on Form S-6
         (Registration Nos. 33-02389, 33-03180, 33-04508, 33-05571, and
         33-06441, respectively) under the Act.
       
        
<PAGE>

                        INSURED MUNICIPAL SECURITIES TRUST
                        17TH DISCOUNT SERIES AND SERIES 6,
                               18TH DISCOUNT SERIES,
                        19TH DISCOUNT SERIES AND SERIES 7,
                    20TH DISCOUNT SERIES, 21ST DISCOUNT SERIES

                               CROSS-REFERENCE SHEET

                       Pursuant to Rule 404 of Regulation C
                         under the Securities Act of 1933

                   (Form N-8B-2 Items required by Instruction as
                          to the Prospectus in Form S-6)


                 Form N-8B-2                                   Form S-6
                 Item Number                            Heading in Prospectus


                     I.  Organization and General Information

     1.  (a) Name of trust...................    Front Cover of Prospectus
         (b) Title of securities issued......      "
     2.  Name and address of each depositor..    The Sponsor
     3.  Name and address of trustee.........    The Trustee
     4.  Name and address of principal
           underwriters......................    The Sponsor
     5.  State of organization of trust......    Organization
     6.  Execution and termination of
           trust agreement...................    Trust Agreement, Amendment and
                                                   Termination
     7.  Changes of name.....................    Not Applicable
     8.  Fiscal year.........................      "
     9.  Litigation..........................    None


         II.  General Description of the Trust and Securities of the Trust

    10.  (a) Registered or bearer
             securities......................    Certificates
         (b) Cumulative or distributive
             securities......................    Interest and Principal
                                                   Distributions 
         (c) Redemption......................    Trustee Redemption
         (d) Conversion, transfer, etc.......    Certificates, Sponsor
                                                   Repurchase, Trustee
                                                   Redemption, Exchange 
                                                   Privilege and Conversion
                                                   Offer
         (e) Periodic payment plan...........    Not Applicable
         (f) Voting rights...................    Trust Agreement, Amendment and
                                                   Termination
         (g) Notice to certificateholders....    Records, Portfolio, Trust
                                                   Agreement, Amendment and
                                                   Termination, The Sponsor, The
                                                   Trustee
         (h) Consents required...............    Trust Agreement, Amendment and
                                                   Termination
         (i) Other provisions................    Tax Status
    11.  Type of securities
           comprising units..................    Objectives, Portfolio,
                                                   Description of Portfolio
    12.  Certain information regarding
           periodic payment certificates.....    Not Applicable
    13.  (a) Load, fees, expenses, etc.......    Summary of Essential
                                                   Information, Offering Price,
                                                   Volume and Other Discounts,
                                                   Sponsor's and Underwriters'
                                                   Profits, Total Reinvestment
                                                   Plan, Trust Expenses and
                                                   Charges
         (b) Certain information regarding
             periodic payment certificates...    Not Applicable
         (c) Certain percentages.............    Summary of Essential
                                                   Information, Offering Price,
                                                   Total Reinvestment Plan
         (d) Price differences...............    Volume and Other Discounts
         (e) Other loads, fees, expenses.....    Certificates
         (f) Certain profits receivable
             by depositors, principal
             underwriters, trustee or
             affiliated persons..............    Sponsor's and Underwriters'
                                                   Profits
         (g) Ratio of annual charges
             to income.......................    Not Applicable
    14.  Issuance of trust's securities......    Organization, Certificates
    15.  Receipt and handling of payments
           from purchasers...................    Organization
    16.  Acquisition and disposition of
           underlying securities.............    Organization, Objectives,
                                                   Portfolio, Portfolio
                                                   Supervision
    17.  Withdrawal or redemption............    Comparison of Public Offering
                                                   Price, Sponsor's Repurchase
                                                   Price and Redemption Price,
                                                   Sponsor Repurchase, Trustee
                                                   Redemption
    18.  (a) Receipt, custody and
             disposition of income...........    Distribution Elections,
                                                   Interest and Principal
                                                   Distributions, Records,
                                                   Total Reinvestment Plan
         (b) Reinvestment of distributions...    Total Reinvestment Plan
         (c) Reserves or special funds.......    Interest and Principal
                                                   Distributions
         (d) Schedule of distributions.......    Not Applicable
    19.  Records, accounts and reports.......    Records, Total Reinvestment
                                                   Plan
    20.  Certain miscellaneous provisions
           of trust agreement................    Trust Agreement, Amendment and
                                                   Termination
         (a) Amendment.......................      "
         (b) Termination.....................      "
         (c) and (d) Trustee, removal and
             successor.......................    The Trustee
         (e) and (f) Depositor, removal
             and successor...................    The Sponsor
    21.  Loans to security holders...........    Not Applicable
    22.  Limitations on liability............    The Sponsor, The Trustee,
                                                   The Evaluator
    23.  Bonding arrangements................    Part II--Item A
    24.  Other material provisions
           of trust agreement................    Not Applicable


         III.  Organization, Personnel and Affiliated Persons of Depositor

    25.  Organization of depositor...........    The Sponsor
    26.  Fees received by depositor..........    Not Applicable
    27.  Business of depositor...............    The Sponsor
    28.  Certain information as to
           officials and affiliated
           persons of depositor..............    Part II--Item C
    29.  Voting securities of depositor......    Not Applicable
    30.  Persons controlling depositor.......      "
    31.  Payments by depositor for certain
           services rendered to trust........      "
    32.  Payment by depositor for certain
           other services rendered to trust..      "
    33.  Remuneration of employees of
         depositor for certain services
         rendered to trust...................      "
    34.  Remuneration of other persons for
         certain services rendered to trust..      "


                  IV.  Distribution and Redemption of Securities

    35.  Distribution of trust's
           securities by states..............    Distribution of Units
    36.  Suspension of sales of
           trust's securities................    Not Applicable
    37.  Revocation of authority
           to distribute.....................      "
    38.  (a) Method of distribution..........    Distribution of Units, Total
                                                   Reinvestment Plan
         (b) Underwriting agreements.........      "
         (c) Selling agreements..............      "
    39.  (a) Organization of principal
             underwriters....................    The Sponsor
         (b) N.A.S.D. membership of
             principal underwriters..........      "
    40.  Certain fees received by
           principal underwriters............    Not Applicable
    41.  (a) Business of principal
             underwriters....................    The Sponsor
         (b) Branch offices of principal
             underwriters....................    Not Applicable
         (c) Salesmen of principal
             underwriters....................      "
    42.  Ownership of trust's
           securities by certain persons.....      "
    43.  Certain brokerage commissions
           received by principal
           underwriters......................      "
    44.  (a) Method of valuation.............    Summary of Essential
                                                   Information, Offering Price,
                                                   Accrued Interest, Volume and
                                                   Other Discounts, Total
                                                   Reinvestment Plan,
                                                   Distribution of Units
         (b) Schedule as to offering price...    Not Applicable
         (c) Variation in offering price
             to certain persons..............    Distribution of Units, Total
                                                   Reinvestment Plan, Volume and
                                                   Other Discounts
    45.  Suspension of redemption rights.....    Trustee Redemption

    46.  (a) Redemption valuation............    Comparison of Public Offering
                                                   Price, Sponsor's Repurchase
                                                   Price and Redemption Price,
                                                   Trustee Redemption
         (b) Schedule as to
             redemption price................    Not Applicable
    47.  Maintenance of position in
           underlying securities.............    Comparison of Public Offering
                                                   Price, Sponsor's Repurchase
                                                   Price and Redemption Price,
                                                   Sponsor Repurchase, Trustee
                                                   Redemption


                V.  Information Concerning the Trustee or Custodian

    48.  Organization and regulation
           of trustee........................    The Trustee
    49.  Fees and expenses of trustee........    Trust Expenses and Charges
    50.  Trustee's lien......................      "


          VI.  Information Concerning Insurance of Holders of Securities

    51.  Insurance of holders of
           trust's securities................    Not Applicable


                            VII.  Policy of Registrant

    52.  (a) Provisions of trust agreement
             with respect to selection or
             elimination of underlying
             securities......................    Objectives, Portfolio,
                                                   Portfolio Supervision
         (b) Transactions involving
             elimination of underlying
             securities......................    Not Applicable
         (c) Policy regarding substitution
             or elimination of underlying
             securities......................    Objectives, Portfolio,
                                                 Portfolio Supervision,
                                                 Substitution of Bonds
         (d) Fundamental policy not
             otherwise covered...............    Not Applicable
    53.  Tax status of trust.................    Tax Status


                   VIII.  Financial and Statistical Information

    54.  Trust's securities during
           last ten years....................    Not Applicable
    55.  Hypothetical account for issuers
           of periodic payment plans.........      "
    56.  Certain information regarding
           periodic payment certificates.....      "
    57.  Certain information regarding
           periodic payment plans............      "
    58.  Certain other information
           regarding periodic payment plans..      "
    59.  Financial Statements
         (Instruction 1(c) to Form S-6)......    Statement of Financial
                                                   Condition
<PAGE>




                 NOTE:  Part A of This Prospectus May Not Be     
                        Distributed Unless Accompanied by Part B.


                        INSURED MUNICIPAL SECURITIES TRUST

                               17TH DISCOUNT SERIES
                              (MULTIPLIER PORTFOLIO)


                                                                              
       
          The Trust is a unit investment trust designated 17th Discount Series
    ("Insured Municipal Discount Trust") with an underlying portfolio of long-
    term insured tax-exempt bonds issued by or on behalf of states,
    municipalities and public authorities and was formed to preserve capital
    and to provide interest income (including, where applicable, earned
    original issue discount) which, in the opinions of bond counsel to the
    respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law but may be subject to state
    and local taxes.  Capital gains are subject to tax.  (See "Tax Status" and
    "The Trust--Portfolio" in Part B of this Prospectus.)  The Sponsor is
    Bear, Stearns & Co. Inc.  The value of the Units of the Trust will
    fluctuate with the value of the underlying bonds.  Minimum purchase:  1
    Unit. 

                                                                              


          This Prospectus consists of two parts.  Part A contains the Summary
    of Essential Information as of December 31, 1993 (the "Evaluation Date"),
    a summary of certain specific information regarding the Trust and audited
    financial statements of the Trust, including the related portfolio, as of
    the Evaluation Date.  Part B of this Prospectus contains a general summary
    of the Trust. 
        
                    Investors should retain both parts of this
                         Prospectus for future reference. 

                                                                              


     THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES
     AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE
     COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR
     ADEQUACY OF THIS PROSPECTUS.  ANY REPRESENTATION TO THE CONTRARY IS A
     CRIMINAL OFFENSE.

       
                      Prospectus Part A Dated April 29, 1994
        


    <PAGE>
       
          THE TRUST.  The Trust is a unit investment trust formed to preserve
    capital and to provide interest income (including, where applicable,
    earned original issue discount) which, in the opinions of bond counsel to
    the respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law through investment in a
    fixed, diversified portfolio of long-term insured bonds (the "Bonds")
    issued by or on behalf of states, municipalities and public authorities
    which, because of irrevocable insurance, are rated "AAA" by Standard &
    Poor's Corporation.  Although the Supreme Court has determined that
    Congress has the authority to subject interest on bonds such as the Bonds
    in the Trust to regular federal income taxation, existing law excludes
    such interest from regular federal income tax.  Such interest income may,
    however, be subject to the federal corporate alternative minimum tax and
    to state and local taxes.  (See "Tax Status" in Part B of this
    Prospectus.)  For a list of ratings on the Evaluation Date, see
    "Portfolio."  The Bonds were acquired at prices which resulted in the
    portfolio as a whole being purchased at a deep discount from par value. 
    The portfolio may also include bonds issued at an original issue discount. 
    Additionally, some of the Bonds in the portfolio may be "Zero Coupon
    Bonds," which are original issue discount bonds that provide for payment
    at maturity at par value, but do not provide for the payment of any
    current interest.  Some of the Bonds in the Trust have been issued with
    optional refunding or refinancing provisions ("Refunded Bonds") whereby
    the issuer of the Bond has the right to call such Bond prior to its stated
    maturity date (and other than pursuant to sinking fund provisions) and to
    issue new bonds ("Refunding Bonds") in order to finance the redemption. 
    Issuers typically utilize refunding calls in order to take advantage of
    lower interest rates in the marketplace.  Some of these Refunded Bonds may
    be called for redemption pursuant to pre-refunding provisions ("Pre-
    Refunded Bonds") whereby the proceeds from the issue of the Refunding
    Bonds are typically invested in government securities in escrow for the
    benefit of the holders of the Pre-Refunded Bonds until the refunding call
    date.  Usually, Pre-Refunded Bonds will bear a triple-A rating because of
    this escrow.  The issuers of Pre-Refunded Bonds must call such Bonds on
    their refunding call date.  Therefore, as of such date, the Trust will
    receive the call price for such bonds but will cease receiving interest
    income with respect to them.  For a list of those Bonds which are Pre-
    Refunded Bonds, if any, as of the Evaluation Date, see "Notes to Financial
    Statements" in this Part A.  Some of the Bonds in the portfolio may have
    been purchased at an aggregate premium over par.  All of the Bonds in the
    Trust were rated "AAA" by Standard & Poor's Corporation at the time
    originally deposited in the Trust.  This rating results from insurance
    relating only to the Bonds in the Trust and not to the Units of the Trust. 
    The insurance does not remove market risk, as it does not guarantee the
    market value of the Units.  For a discussion of the significance of such
    ratings, see "Description of Bond Ratings" in Part B of this Prospectus,
    and for a list of ratings on the Evaluation Date see the "Portfolio."  The
    payment of interest and preservation of capital are, of course, dependent
    upon the continuing ability of issuers of the Bonds or the insurers
    thereof to meet their obligations.  There can be no assurance that the
    Trust's investment objectives will be achieved.  Investment in the Trust
    should be made with an understanding of the risks which an investment in
    long-term fixed rate debt obligations may entail, including the risk that
    the value of the underlying portfolio will decline with increases in
    interest rates, and that the value of Zero Coupon Bonds is subject to
    greater fluctuation than coupon bonds in response to changes in interest
    rates.  Each Unit in the Trust represents a 1/12000th undivided interest
    in the principal and net income of the Trust.  The principal amount of
    Bonds deposited in the Trust per Unit is reflected in the Summary of
    Essential Information.  (See "Organization" in Part B of this Prospectus.) 
    The Units being offered hereby are issued and outstanding Units which have
    been purchased by the Sponsor in the secondary market. 

          INSURANCE.  Each of the Bonds in the Trust is insured by a municipal
    bond guaranty insurance policy obtained by either the Sponsor ("Sponsor-
    Insured Bonds") or the issuers of the Bonds ("Pre-Insured Bonds") and
    issued by one of the insurance companies (the "Insurance Companies"),
    described under "Insurance on the Bonds" in Part B of this Prospectus,
    covering scheduled payment of principal thereof and interest thereon when
    such amounts shall become due for payment but shall not have been paid by
    the issuer or any other insurer thereof.  The insurance, unless obtained
    by Municipal Bond Investors Assurance Corporation ("MBIA Corp."), will
    also cover any accelerated payments of principal and the increase in
    interest payments or premiums, if any, payable upon mandatory redemption
    of the Bonds if interest on any Bonds is ultimately deemed to be subject
    to regular federal income tax.  Insurance obtained from MBIA Corp. only
    guarantees the accelerated payments required to be made by or on behalf of
    an issuer of small industrial revenue bonds and pollution control bonds if
    there is an event which results in the loss of tax-exempt status of the
    interest on such Bonds, including principal, interest or premium payments,
    if any, as and when required.  To the extent, therefore, that Bonds are
    only covered by insurance obtained from MBIA Corp., such Bonds will not be
    covered for the accelerated payments required to be made by or on behalf
    of an issuer of other than small industrial revenue bonds or pollution
    control revenue bonds if there occurs an event which results in the loss
    of tax-exempt status of the interest on such Bonds.  None of the insurance
    will cover accelerated payments of principal or penalty interest or
    premiums unrelated to taxability of interest on the Bonds (although the
    insurance, including insurance obtained by MBIA Corp., does guarantee
    payment of principal and interest in such amounts and at such times as
    such amounts would have been due absent such acceleration).  The insurance
    relates only to the prompt payment of principal of and interest on the
    securities in the portfolio, and does not remove market risks or guarantee
    the market value of the Units in the Trust.  The terms of the insurance
    are more fully described under "Insurance on the Bonds" in Part B of this
    Prospectus.  For a discussion of the effect of an occurrence of nonpayment
    of principal or interest on any Bonds in the Trust, see "Portfolio
    Supervision" in Part B of this Prospectus.  No representation is made
    herein as to any Bond insurer's ability to meet its obligations under a
    policy of insurance relating to any of the Bonds.  In addition, investors
    should be aware that, subsequent to the Date of Deposit, the rating of the
    claims-paying ability of the insurer of an underlying Bond may be
    downgraded, which may result in a downgrading of the rating of the Units
    in the Trust.  The approximate percentage of the aggregate principal
    amount of the portfolio that is insured by each Insurance Company is as
    follows:  AMBAC Indemnity Corp. ("AMBAC"), 6.3%; Bond Investors Guaranty
    ("BIG"), 5.3%; Financial Guaranty Insurance Company ("Financial
    Guaranty"), 16.4%, Firemen's Fund Insurance ("Firemen's"), 4.6% and
    Municipal Bond Insurance Association ("MBIA"), 67.4%. 

          PUBLIC OFFERING PRICE.  The secondary market Public Offering Price
    of each Unit is equal to the aggregate bid price of the Bonds in the Trust
    divided by the number of Units outstanding, plus a sales charge of 5.5% of
    the Public Offering Price, or 5.820% of the net amount invested in Bonds
    per Unit.  In addition, accrued interest to the expected date of
    settlement, including earned original issue discount, is added to the
    Public Offering Price.  If Units had been available for sale on the
    Evaluation Date, the Public Offering Price per Unit would have been
    $507.92 plus accrued interest of $7.39 under the monthly distribution
    plan, $10.47 under the semi-annual distribution plan and $10.49 under the
    annual distribution plan, for a total of $515.31, $518.39 and $518.41,
    respectively.  The Public Offering Price per Unit can vary on a daily
    basis in accordance with fluctuations in the aggregate bid price of the
    Bonds.  (See "Public Offering--Offering Price" in Part B of this
    Prospectus.)

          ESTIMATED LONG TERM RETURN AND ESTIMATED CURRENT RETURN.  The rate
    of return on an investment in Units of the Trust is measured in terms of
    "Estimated Current Return" and "Estimated Long Term Return".

          Estimated Long Term Return is calculated by:  (1) computing the
    yield to maturity or to an earlier call date (whichever results in a lower
    yield) for each Bond in the Trust's portfolio in accordance with accepted
    bond practices, which practices take into account not only the interest
    payable on the Bond but also the amortization of premiums or accretion of
    discounts, if any; (2) calculating the average of the yields for the Bonds
    in the Trust's portfolio by weighing each Bond's yield by the market value
    of the Bond and by the amount of time remaining to the date to which the
    Bond is priced (thus creating an average yield for the portfolio of the
    Trust); and (3) reducing the average yield for the portfolio of the Trust
    in order to reflect estimated fees and expenses of the Trust and the
    maximum sales charge paid by investors.  The resulting Estimated Long Term
    Return represents a measure of the return to investors earned over the
    estimated life of the Trust.  (For the Estimated Long Term Return to
    Certificateholders under the monthly, semi-annual and annual distribution
    plans, see "Summary of Essential Information".)

          Estimated Current Return is a measure of the Trust's cash flow. 
    Estimated Current Return is computed by dividing the Estimated Net Annual
    Interest Income per Unit by the Public Offering Price per Unit.  In
    contrast to the Estimated Long Term Return, the Estimated Current Return
    does not take into account the amortization of premium or accretion of
    discount, if any, on the Bonds in the portfolio of the Trust.  Moreover,
    because interest rates on Bonds purchased at a premium are generally
    higher than current interest rates on newly issued bonds of a similar type
    with comparable rating, the Estimated Current Return per Unit may be
    affected adversely if such Bonds are redeemed prior to their maturity.

          The Estimated Net Annual Interest Income per Unit of the Trust will
    vary with changes in the fees and expenses of the Trustee and the
    Evaluator applicable to the Trust and with the redemption, maturity, sale
    or other disposition of the Bonds in the Trust.  The Public Offering Price
    will vary with changes in the bid prices of the Bonds.  Therefore, there
    is no assurance that the present Estimated Current Return or Estimated
    Long Term Return will be realized in the future.  (For the Estimated
    Current Return to Certificateholders under the monthly, semi-annual and
    annual distribution plans, see "Summary of Essential Information".  See
    "Estimated Long Term Return and Estimated Current Return" in Part B of
    this Prospectus.)

          A schedule of cash flow projections is available from the Sponsor
    upon request.

          DISTRIBUTIONS.  Distributions of interest income, less expenses,
    will be made by the Trust either monthly, semi-annually or annually
    depending upon the plan of distribution applicable to the Unit purchased. 
    A purchaser of a Unit in the secondary market will initially receive
    distributions in accordance with the distribution plan chosen by the prior
    owner of such Unit and may thereafter change the plan as provided under
    "Interest and Principal Distributions" in Part B of this Prospectus. 
    Distributions of principal, if any, will be made semi-annually on June 15
    and December 15 of each year.  (See "Rights of Certificateholders--
    Interest and Principal Distributions" in Part B of this Prospectus.  For
    estimated monthly, semi-annual and annual interest distributions, see
    "Summary of Essential Information.")

          MARKET FOR UNITS.  The Sponsor, although not obligated to do so,
    presently maintains and intends to continue to maintain a secondary market
    for the Units at prices based on the aggregate bid price of the Bonds in
    the Trust portfolio.  The reoffer price will be based on the aggregate bid
    price of the Bonds plus a sales charge of 5.5% of the Public Offering
    Price (5.820% of the net amount invested), plus net accrued interest.  If
    a market is not maintained a Certificateholder will be able to redeem his
    Units with the Trustee at a price also based on the aggregate bid price of
    the Bonds.  (See "Liquidity--Sponsor Repurchase" and "Public Offering--
    Offering Price" in Part B of this Prospectus.)
        
          TOTAL REINVESTMENT PLAN.  Certificateholders under the semi-annual
    and annual plans of distribution have the opportunity to have all their
    regular interest distributions, and principal distributions, if any,
    reinvested in available series of "Insured Municipal Securities Trust" or
    "Municipal Securities Trust."  (See "Total Reinvestment Plan" in Part B of
    this Prospectus.  Residents of Texas see "Total Reinvestment Plan for
    Texas Residents" in Part B of this Prospectus.)  The Plan is not designed
    to be a complete investment program. 


    <PAGE>
       
                        INSURED MUNICIPAL SECURITIES TRUST
                               17TH DISCOUNT SERIES

             SUMMARY OF ESSENTIAL INFORMATION AS OF DECEMBER 31, 1993

    Date of Deposit:  January 30, 1986         Minimum Principal Distribution:
    Principal Amount of Bonds ...$10,875,000    $1.00 per Unit.
    Number of Units .............12,000        Weighted Average Life to
    Fractional Undivided Inter-                Maturity:
      est in Trust per Unit .....1/12000        17.1 Years.
    Principal Amount of                        Minimum Value of Trust:
      Bonds per Unit ............$906.25        Trust may be terminated if
    Secondary Market Public                     value of Trust is less than
      Offering Price**                          $4,800,000 in principal amount
      Aggregate Bid Price                       of Bonds.
        of Bonds in Trust .......$5,759,735+++ Mandatory Termination Date:
      Divided by 12,000 Units ...$479.98        The earlier of December 31,
      Plus Sales Charge of 5.5%                 2035 or the disposition of the
        of Public Offering Price $27.94         last Bond in the Trust.
      Public Offering Price                    Trustee***:  United States Trust 
        per Unit ................$507.92+       Company of New York.
    Redemption and Sponsor's                   Trustee's Annual Fee:  Monthly 
      Repurchase Price                          plan $1.03 per $1,000; semi-
      per Unit ..................$479.98+       annual plan $.55 per $1,000;
                                        +++     and annual plan is $.36 per
                                        ++++    $1,000.
    Excess of Secondary Market                 Evaluator:  Kenny S&P Evaluation
      Public Offering Price                     Services. 
      over Redemption and                      Evaluator's Fee for Each
      Sponsor's Repurchase                      Evaluation:  Minimum of $12
      Price per Unit ............$27.94++++     plus $.25 per each issue of
    Difference between Public                   Bonds in excess of 50 issues
      Offering Price per Unit                   (treating separate maturities
      and Principal Amount per                  as separate issues).
      Unit Premium/(Discount) ...$(398.33)     Sponsor:  Bear, Stearns & Co.
    Evaluation Time:  4:00 p.m.                Inc.
      New York Time.                           Sponsor's Annual Fee:  Maximum of
                                                $.15 per $1,000 principal
                                                amount of Bonds (see "Trust
                                                Expenses and Charges" in Part B
                                                of this Prospectus).

        PER UNIT INFORMATION BASED UPON INTEREST DISTRIBUTION PLAN ELECTED

                                            Monthly   Semi-Annual   Annual
                                            Option      Option      Option


    Gross annual interest income# .........$38.51       $38.51     $38.51
    Less estimated annual fees and
      expenses ............................  1.62         1.03        .83
    Estimated net annual interest          ______       ______     ______
      income (cash)# ......................$36.89       $37.48     $37.68
    Estimated interest distribution# ......  3.07        18.74      37.68
    Estimated daily interest accrual# ..... .1024        .1041      .1046
    Estimated current return#++ ........... 7.26%        7.38%      7.42%
    Estimated long term return++ .......... 3.28%        3.40%      3.44%
    Record dates .......................... 1st of     Dec. 1 and   Dec. 1
                                            each month June 1
    Interest distribution dates ........... 15th of    Dec. 15 and  Dec. 15
                                            each month June 15
        
    <PAGE>
       *  The Date of Deposit is the date on which the Trust Agreement was
          signed and the deposit of the Bonds with the Trustee made.

      **  For information regarding offering price per Unit and applicable
          sales charge under the Total Reinvestment Plan, see "Total
          Reinvestment Plan" in Part B of this Prospectus. 

     ***  The Trustee maintains its corporate trust office at 770 Broadway,
          New York, New York 10003 (tel. no. 1-800-428-8890).  For information
          regarding redemption by the trustee, see "Trustee Redemption" in
          Part B of this Prospectus.
       
       +  Plus accrued interest to the expected date of settlement
          (approximately five business days after purchase) of $7.39 monthly,
          $10.47 semi-annually and $10.49 annually. 
        
      ++  The estimated current return and estimated long term return are
          increased for transactions entitled to a discount (see "Employee
          Discounts" in Part B of this Prospectus), and are higher under the
          semi-annual and annual options due to lower Trustee's fees and
          expenses.

     +++  Based solely upon the bid side evaluation of the underlying Bonds
          (including, where applicable, undistributed cash from the principal
          account).  Upon tender for redemption, the price to be paid will be
          calculated as described under "Trustee Redemption" in Part B of this
          Prospectus. 

    ++++  See "Comparison of Public Offering Price, Sponsor's Repurchase Price
          and Redemption Price" in Part B of this Prospectus. 

       #  Does not include income accrual from original issue discount bonds,
          if any.

    <PAGE>
       
                          INFORMATION REGARDING THE TRUST
                              AS OF DECEMBER 31, 1993


    DESCRIPTION OF PORTFOLIO*

          The portfolio of the Trust consists of 15 issues representing
    obligations of issuers located in 12 states and the District of Columbia. 
    The Sponsor has not participated as a sole underwriter or manager, co-
    manager or member of an underwriting syndicate from which any of the
    initial aggregate principal amount of the Bonds were acquired. 
    Approximately 54.8% of the Bonds are obligations of state and local
    housing authorities; approximately 17.7% are hospital revenue bonds;
    approximately 11.8% were issued in connection with the financing of
    nuclear generating facilities; and none are "mortgage subsidy" bonds.  All
    of the Bonds in the Trust are subject to redemption prior to their stated
    maturity dates pursuant to sinking fund or optional call provisions.  The
    Bonds may also be subject to other calls, which may be permitted or
    required by events which cannot be predicted (such as destruction,
    condemnation, termination of a contract, or receipt of excess or
    unanticipated revenues).  None of the Bonds are general obligation bonds. 
    Fifteen issues representing $10,875,000 of the principal amount of the
    Bonds are payable from the income of a specific project or authority and
    are not supported by the issuer's power to levy taxes.  The portfolio is
    divided for purpose of issue as follows:  Coal Power 1, Federally Insured
    Mortgage 2, Hospital 4, Industrial Development 1, Levee District 1, Multi-
    Family Housing 1, Nuclear Power 3, Waste Water 1 and Water 1.  For an
    explanation of the significance of these factors see "The Trust--
    Portfolio" in Part B of this Prospectus. 

    *     Changes in the Trust Portfolio:  From January 1, 1994 to March 24,
          1994, the entire principal amount of the Bonds in portfolio no. 14
          has been called and is no longer contained in the Trust.  35 Units
          have been redeemed from the Trust.

    <PAGE>

          As of December 31, 1993, $5,935,000 (approximately 54.8% of the
    aggregate principal amount of the Bonds) were original issue discount
    bonds.  Of these original issue discount bonds, $5,935,000 (approximately
    54.8% of the aggregate principal amount of the Bonds) were Zero Coupon
    Bonds.  Zero Coupon Bonds do not provide for the payment of any current
    interest and provide for payment at maturity at par value unless sooner
    sold or redeemed.  The market value of Zero Coupon Bonds is subject to
    greater fluctuations than coupon bonds in response to changes in interest
    rates.  None of the aggregate principal amount of the Bonds in the Trust
    were purchased at a "market" discount from par value at maturity,
    approximately 45.2% were purchased at a premium and none were purchased at
    par.  For an explanation of the significance of these factors see
    "Discount and Zero Coupon Bonds" in Part B of this Prospectus. 

          None of the Bonds in the Trust are subject to the federal individual
    alternative minimum tax under the Tax Reform Act of 1986.  See "Tax
    Status" in Part B of this Prospectus. 

        
    <PAGE>
                       FINANCIAL AND STATISTICAL INFORMATION


    Selected data for each Unit outstanding for the periods listed below:

                                                                    Distribu-
                                                                    tions of
                                          Distributions of Interest Principal
                                          During the Period (per Unit)  During
                               Net Asset *           Semi-             the
                    Units Out-   Value    Monthly   Annual  Annual  Period
    Period Ended     standing  Per Unit   Option    Option  Option (Per Unit)

       
    December 31, 1991 12,000   $510.21    $37.39   $37.95   $38.16  $1.25
    December 31, 1992 12,000    503.81     37.32    37.96    38.16    -0-
    December 31, 1993 12,000    490.66     37.06    37.71    37.91   5.42
        
    *     Net Asset Value per Unit is calculated by dividing net assets as
          disclosed in the "Statement of Net Assets" by the number of Units
          outstanding as of the date of the Statement of Net Assets.  See
          Note 5 of Notes to Financial Statements for a description of the
          components of Net Assets.

    <PAGE>


Independent Auditors' Report


The Sponsor, Trustee and Certificateholders
Insured Municipal Securities Trust, 17th Discount Series:


We have audited the accompanying statement of net assets, including the
portfolio, of Insured Municipal Securities Trust, 17th Discount Series as
of December 31, 1993, and the related statements of operations, and
changes in net assets for each of the years in the three year period then
ended.  These financial statements are the responsibility of the Trustee
(see note 2).  Our responsibility is to express an opinion on these
financial statements based on our audits.

We conducted our audits in accordance with generally accepted auditing
standards.  Those standards require that we plan and perform the audit to
obtain reasonable assurance about whether the financial statements are
free of material misstatement.  An audit includes examining, on a test
basis, evidence supporting the amounts and disclosures in the financial
statements.  Our procedures included confirmation of securities owned as
of December 31, 1993, by correspondence with the Trustee.  An audit also
includes assessing the accounting principles used and significant estimates
made by management, as well as evaluating the overall financial statement
presentation.  We believe that our audits provide a reasonable basis for
our opinion.

In our opinion, the financial statements referred to above present fairly,
in all material respects, the financial position of Insured Municipal
Securities Trust, 17th Discount Series as of December 31, 1993, and the
results of its operations and the changes in its net assets for each of
the years in the three year period then ended in conformity with generally
accepted accounting principles.




    KPMG Peat Marwick


New York, New York
March 31, 1994
<PAGE>


                              Statement of Net Assets

                                December 31, 1993   

Investments in marketable securities,        
at market value (cost $5,693,117)                    $    5,759,736
                              
Excess of other assets over total liabilities               128,209
                                                      -------------
                              
Net assets 12,000 units of fractional undivided                            
interest outstanding, $490.66 per unit)              $    5,887,945
                                                      =============
                              
See accompanying notes to financial statements.                 


<PAGE>

<TABLE>
                              Statements of Operations 

<CAPTION>
                                                              Years ended December 31,
                                                       ---------  --- --------- --- --------
                                                         1993           1992          1991
                                                       ---------      ---------     --------
<S>                                                 <C>                <C>          <C>
     Investment income - interest                   $   486,620        487,846      486,289
                                                       ---------      ---------     --------
                                
     Expenses:                  
        Trustee's fees                                   13,111         12,069       10,938
        Evaluator's fees                                  2,669          2,466        2,079
        Sponsor's advisory fee                            1,641          1,642        1,642
                                                       ---------      ---------     --------
                                
                   Total expenses                        17,421         16,177       14,659
                                                       ---------      ---------     --------
                                
                   Investment income, net               469,199        471,669      471,630
                                                       ---------      ---------     --------
                                
     Realized and unrealized gain
       (loss) on investments:   
          Net realized loss on  
            bonds sold or called                         (4,435)          -            (841)
          Unrealized appreciation
           (depreciation) for the year                 (110,199)       (97,885)     128,061
                                                       ---------      ---------     --------
                                
                Net gain (loss) 
                  on investments                       (114,634)       (97,885)     127,220
                                                       ---------      ---------     --------
                                
                Net increase in net
                  assets resulting
                  from operations                   $   354,565        373,784      598,850
                                                       =========      =========     ========

     See accompanying notes to financial statements.
</TABLE>


<PAGE>

<TABLE>
                            Statements of Changes in Net Assets
      
<CAPTION>
                                                                     Years ended December 31,
                                                          ------------ --- ------------  --- ----------
                                                              1993             1992             1991
                                                          ------------     ------------      ----------
<S>                                                     <C>                <C>               <C>
     Operations:                            
        Investment income, net                          $     469,199          471,669         471,630
        Net realized loss on                
          bonds sold or called                                 (4,435)          -                 (841)
        Unrealized appreciation             
         (depreciation) for the year                         (110,199)         (97,885)        128,061
                                                          ------------     ------------      ----------
     
                     Net increase in net    
                        assets resulting    
                        from operations                       354,565          373,784         598,850
                                                          ------------     ------------      ----------
     
     Distributions to Certificateholders:   
          Investment income                                   447,340          450,520         451,075
          Principal                                            65,040           -               15,000
                                                          ------------     ------------      ----------
     
                     Total distributions                      512,380          450,520         466,075
                                                          ------------     ------------      ----------
     
                     Total increase (decrease)               (157,815)         (76,736)        132,775
     
     Net assets at beginning of year                        6,045,760        6,122,496       5,989,721
                                                          ------------     ------------      ----------
     
     Net assets at end of year (including   
        undistributed net investment        
        income of    $253,725,  $231,866 and
        $210,717 respectively)                          $   5,887,945        6,045,760       6,122,496
                                                          ============     ============      ==========

     See accompanying notes to financial statements.       

</TABLE>

<PAGE>

INSURED MUNICIPAL SECURITIES TRUST, 17TH DISCOUNT SERIES

Notes to Financial Statements

December 31, 1993, 1992 and 1991


(1)    Organization

Insured Municipal Securities Trust, 17th Discount Series (Trust) was
organized on January 30, 1986 by Bear, Stearns & Co. Inc. (Sponsor)
under the laws of the State of New York by a Trust Indenture and
Agreement, and is registered under the Investment Company Act
of 1940.

(2)    Summary of Significant Accounting Policies

United States Trust Company of New York (Trustee) has custody of and
responsibility for the accounting records and financial statements of
the Trust and is responsible for establishing and maintaining a
system of internal control related thereto.

The Trustee is also responsible for all estimates of expenses and
accruals reflected in the Trust's financial statements.  The
accompanying financial statements have been adjusted to record the
unrealized appreciation (depreciation) of investments and to record
interest income and expenses on the accrual basis.

The discount on the zero-coupon bonds is accreted by the interest
method over the respective lives of the bonds.  The accretion of such
discount is included in interest income; however, it is not
distributed until realized in cash upon maturity or sale of the
respective bonds.

Investments are carried at market value which is determined by either
Standard & Poor's Corporation or Moody's Investors Service, Inc.
(Evaluator) as discussed in Footnotes to Portfolio.  The market value
of the investments is based upon the bid prices for the bonds at the
end of the period, except that the market value on the date of
deposit represents the cost to the Trust based on the offering prices
for investments at that date.  The difference between cost (including
accumulated accretion of original issue discount on zero-coupon
bonds) and market value is reflected as unrealized appreciation
(depreciation) of investments.  Securities transactions are recorded
on the trade date.  Realized gains (losses) from securities
transactions are determined on the basis of average cost of the
securities sold or redeemed.

(3)    Income Taxes

The Trust is not subject to Federal income taxes as provided for by
the Internal Revenue Code.

(4)    Trust Administration

The fees and expenses of the Trust are incurred and paid on the basis
set forth under "Trust Expenses and Charges" in Part B of this
Prospectus.

The Trust Indenture and Agreement provides for interest distributions
as often as monthly (depending upon the distribution plan elected by
the
      Certificateholders).

The Trust Indenture and Agreement further requires that principal
received from the disposition of bonds, other than those bonds sold
in connection with the redemption of units, be distributed to
Certificateholders.

See "Financial and Statistical Information" in Part A of this
Prospectus for the amounts of per unit distributions during the years
ended December 31, 1993, 1992, and 1991.

The Trust Indenture and Agreement also requires the Trust to redeem
units tendered.  No units have been redeemed since the inception of
the Trust.

(5)    Net Assets

  At December 31, 1993, the net assets of the Trust represented the
    interest of Certificateholders as follows:

   Original cost to Certificateholders                  $ 7,160,529
   Less initial gross underwriting commission              (393,840)
                                                           6,766,689

    Cost of securities sold or called                    (1,199,087)
    Net unrealized appreciation                              66,619
    Undistributed net investment income                     253,725
    Distribution in excess of proceeds from
     bonds sold or called                                         (1)
      
         Total                                           $ 5,887,945


    The original cost to Certificateholders, less the initial gross
underwriting commission, represents the aggregate initial public offering
price net of the applicable sales charge on 12,000 units of fractional
undivided interest of the Trust as of the date of deposit.

Undistributed net investment income includes accumulated accretion of
original issue discount of $125,515.

<PAGE>

<TABLE>

INSURED MUNICIPAL SECURITIES TRUST, 17TH DISCOUNT SERIES

Portfolio     

December 31, 1993

<CAPTION>


Port-  Aggregate                                   Coupon Rate/   Redemption Feature
folio  Principal       Name of Issuer     Ratings  Date(s) of     S.F.--Sinking Fund         Market
No.     Amount       and Title of Bonds     (1)    Maturity(2)    Ref.--Refunding (2)(7)    Value(3)
- ---   -----------   ---------------------   ----   -----------    ----------------------    ---------
<S>   <C>           <C>                     <C>    <C>            <C>                     <C>
   
1     $   150,000   Municipal Electric      AAA    9.000%         1/01/08 @ 100 S.F.      $   160,863
                    Authority of Georgia           1/01/2020      1/01/95 @ 102 Ref.            
                    Power Revenue Bonds   
                    Series K (AMBAC)      
   
2         525,000   The Hospital            AAA    9.250          10/01/06 @ 100 S.F.         589,297
                    Authority of Walker            10/01/2010     10/01/95 @ 102 Ref.           
                    Dade and Catoosa      
                    Counties (Georgia)    
                    Refunding Revenue     
                    Anticipation          
                    Certificates, 1985    
                    Series (Financial     
                    Guaranty) (5)         
   
3         500,000   Hospital Authority of   AAA    9.250          11/01/06 @ 100 S.F.         563,610
                    St. Joseph County              11/01/2015     11/01/95 @ 102 Ref.           
                    (Indiana) Insured     
                    Hospital Revenue      
                    Bonds, 1985 Series    
                    (Memorial Hospital of 
                    South Bend Project)   
                    (MBIA) (5)            
   
4          20,000   Kentucky Housing        AAA    8.875          1/01/06 @ 100 S.F.           20,692
                    Corporation                    7/01/2019      1/01/96 @ 102 Ref.            
                    Multi-Family Mortgage 
                    Revenue Bonds, 1985   
                    Series A (BIG)        
   
5         500,000   Orleans Louisiana       AAA    9.350          11/01/06 @ 100 S.F.         549,925
                    Levee District Marina          11/01/2015     5/01/95 @ 102 Ref.            
                    Revenue Bonds, 1985   
                    Series (Financial     
                    Guaranty) (5)         
   
6         550,000   Southern Minnesota,     AAA    9.500          No Sinking Fund             624,971
                    Municipal Power                1/01/2017      1/01/96 @ 102 Ref.            
                    Agency Supply System  
                    Revenue Bonds, 1985   
                    Series A (BIG) (5)    
   
7          40,000   Ocean County            AAA    8.700          1/01/07 @ 100 S.F.           44,829
                    Utilities Authority            1/01/2011      1/01/96 @ 102 Ref.            
                    New Jersey Wastewater 
                    Revenue Refunding     
                    Bonds, 1985 Series    
                    (Financial Guaranty)  
                    (5)                   
   
8         500,000   Albuquerque, New        AA-    9.375          12/01/96 @ 100 S.F.         538,880
                    Mexico Industrial              12/01/2005     12/01/94 @ 102 Ref.           
                    Development Bonds for 
                    Capital Glass and     
                    Aluminum Corporation  
                    1985 Series           
                    (Firemen's Fund       
                    Insurance)            
   
9         600,000   City of Farmington,     AAA    9.750          5/15/06 @ 100 S.F.          697,608
                    New Mexico Utility             5/15/2013      5/15/96 @ 102 Ref.            
                    System Revenue Bonds, 
                    1985 Series           
                    (Financial Guaranty)  
                    (5)                   
   
10        535,000   Piedmont Municipal      AAA    9.250          1/01/16 @ 100 S.F.          610,360
                    Power Agency (South            1/01/2019      1/01/96 @ 103 Ref.            
                    Carolina) Electric    
                    Revenue Bonds, 1985   
                    Series  (AMBAC) (5)   
   
   
   
11  $     400,000   Waco (Texas) Health     AAA    9.200%         9/01/06 @ 100 S.F.      $   446,416
                    Facilities                     9/01/2014      9/01/95 @ 102 Ref.            
                    Development           
                    Corporation Hospital  
                    Refunding Revenue     
                    Bonds, 1985 Series    
                    (Hillcrest Baptist    
                    Medical Center        
                    Project) (MBIA) (5)   
   
12        120,000   Burlington, Vermont     AAA    9.750          7/01/01 @ 100 S.F.          135,007
                    Waterworks System              7/01/2005      7/01/95 @ 103 Ref.            
                    Revenue Bonds, 1985   
                    Series A (Financial   
                    Guaranty) (5)         
   
13        500,000   Wisconsin Health        AAA    9.250          7/01/06 @ 100 S.F.          550,670
                    Facility Authority             7/01/2012      7/01/95 @ 102 Ref.            
                    Hospital Revenue      
                    Bonds, Sisters        
                    Services Incorporated 
                    - St. Mary's Hospital 
                    1985 Series (MBIA)    
   
14      3,955,000   The District of         AAA    0.000          5/01/05 @ 11.975 S.F.       159,110
                    Columbia Multi-Unit            11/01/2025     11/01/98 @ 6.415 Ref.         
                    Housing Finance       
                    Corporation Mortgage  
                    Revenue Bonds, Series 
                    1983 (FHA Insured     
                    Mortgage              
                    Loan-Congress Park II 
                    Apartments Section 8  
                    Assisted Project)     
                    (MBIA)                
   
15      1,980,000   Anne Arundel County,    AAA    0.000          6/01/21 @ 54.504 S.F.        67,498
                    Maryland Economic              6/01/2027      1/06/94 @ 3.409 Ref.          
                    Development Revenue   
                    Bonds, Series 1985    
                    (FHA Insured Mortgage 
                    Loan-The Regency Club 
                    II Facility) (MBIA)   
                    (5)                   
      -----------                                                                           ---------
   
    $  10,875,000                                                                         $ 5,759,736
      ===========                                                                           =========

See accompanying footnotes to portfolio and notes to financial statements.
</TABLE>

<PAGE>
                    
INSURED MUNICIPAL SECURITIES TRUST, 17TH DISCOUNT SERIES

Footnotes to Portfolio

December 31, 1993

(1) All ratings are by Standard & Poor's Corporation.  A brief description
of the ratings symbols and their meanings is set forth under
"Description of Bond Ratings" in Part B of this Prospectus.

(2) See "The Trust - Portfolio" in Part B of this Prospectus for an
explanation of redemption features.  See "Tax Status" in Part B of
this Prospectus for a statement of the Federal tax consequences to a
Certificateholder upon the sale, redemption or maturity of a bond.

(3)  At December 31, 1993, the net unrealized appreciation of all the bonds
was comprised of the following:

    Gross unrealized appreciation                      $  85,062
    Gross unrealized depreciation                        (18,443)

               Net unrealized appreciation            $   66,619

(4) The annual interest income, based upon bonds held at December 31, 1993,
(excluding accretion of original issue discount on zero-coupon bonds)
to the Trust is $462,180.

(5) The bonds have been prerefunded and will be redeemed at the next
refunding call date.

(6) Bonds sold or called after December 31, 1993 are noted in a footnote
"Changes in Trust Portfolio" under "Description of Portfolio" in Part
A of this Prospectus.

(7)  The Bonds may also be subject to other calls, which may be permitted
or required by events which cannot be predicted (such as
destruction, condemnation, termination of a contract, or receipt of
excess or unanticipated revenues).
<PAGE>


                 NOTE:  Part A of This Prospectus May Not Be     
                        Distributed Unless Accompanied by Part B.


                        INSURED MUNICIPAL SECURITIES TRUST

                                     SERIES 6

                                                                              
       
          The Trust is a unit investment trust designated Series 6 ("Insured
    Municipal Trust") with an underlying portfolio of long-term insured tax-
    exempt bonds issued by or on behalf of states, municipalities and public
    authorities and was formed to preserve capital and to provide interest
    income (including, where applicable, earned original issue discount)
    which, in the opinions of bond counsel to the respective issuers, is, with
    certain exceptions, currently exempt from regular federal income tax under
    existing law but may be subject to state and local taxes.  Capital gains
    are subject to tax.  (See "Tax Status" and "The Trust--Portfolio" in
    Part B of this Prospectus.)  The Sponsor is Bear, Stearns & Co. Inc.  The
    value of the Units of the Trust will fluctuate with the value of the
    underlying bonds.  Minimum purchase:  1 Unit. 

                                                                              


          This Prospectus consists of two parts.  Part A contains the Summary
    of Essential Information as of December 31, 1993 (the "Evaluation Date"),
    a summary of certain specific information regarding the Trust and audited
    financial statements of the Trust, including the related portfolio, as of
    the Evaluation Date.  Part B of this Prospectus contains a general summary
    of the Trust. 
        
                    Investors should retain both parts of this
                         Prospectus for future reference. 

                                                                              


     THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES
     AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE
     COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR
     ADEQUACY OF THIS PROSPECTUS.  ANY REPRESENTATION TO THE CONTRARY IS A
     CRIMINAL OFFENSE.
       
                      Prospectus Part A Dated April 29, 1994
        


    <PAGE>
       
          THE TRUST.  The Trust is a unit investment trust formed to preserve
    capital and to provide interest income (including, where applicable,
    earned original issue discount) which, in the opinions of bond counsel to
    the respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law through investment in a
    fixed, diversified portfolio of long-term insured bonds (the "Bonds")
    issued by or on behalf of states, municipalities and public authorities
    which, because of irrevocable insurance, are rated "AAA" by Standard &
    Poor's Corporation.  Although the Supreme Court has determined that
    Congress has the authority to subject interest on bonds such as the Bonds
    in the Trust to regular federal income taxation, existing law excludes
    such interest from regular federal income tax.  Such interest income may,
    however, be subject to the federal corporate alternative minimum tax and
    to state and local taxes.  (See "Tax Status" in Part B of this
    Prospectus.)  For a list of ratings on the Evaluation Date, see
    "Portfolio."  Some of the Bonds may be "Zero Coupon Bonds", which are
    original issue discount bonds that provide for payment at maturity at par
    value, but do not provide for the payment of any current interest.  Some
    of the Bonds in the Trust have been issued with optional refunding or
    refinancing provisions ("Refunded Bonds") whereby the issuer of the Bond
    has the right to call such Bond prior to its stated maturity date (and
    other than pursuant to sinking fund provisions) and to issue new bonds
    ("Refunding Bonds") in order to finance the redemption.  Issuers typically
    utilize refunding calls in order to take advantage of lower interest rates
    in the marketplace.  Some of these Refunded Bonds may be called for
    redemption pursuant to pre-refunding provisions ("Pre-Refunded Bonds")
    whereby the proceeds from the issue of the Refunding Bonds are typically
    invested in government securities in escrow for the benefit of the holders
    of the Pre-Refunded Bonds until the refunding call date.  Usually, Pre-
    Refunded Bonds will bear a triple-A rating because of this escrow.  The
    issuers of Pre-Refunded Bonds must call such Bonds on their refunding call
    date.  Therefore, as of such date, the Trust will receive the call price
    for such bonds but will cease receiving interest income with respect to
    them.  For a list of those Bonds which are Pre-Refunded Bonds, if any, as
    of the Evaluation Date, see "Notes to Financial Statements" in this
    Part A.  Some of the Bonds in the portfolio may have been purchased at an
    aggregate premium over par.  All of the Bonds in the Trust were rated
    "AAA" by Standard & Poor's Corporation on the Date of Deposit.  This
    rating results from insurance relating only to the Bonds in the Trust and
    not to Units of the Trust.  The insurance does not remove market risk, as
    it does not guarantee the market value of the Units.  For a discussion of
    the significance of such ratings, see "Description of Bond Ratings" in
    Part B of this Prospectus, and for a list of ratings on the Evaluation
    Date see the "Portfolio."  The payment of interest and preservation of
    capital are, of course, dependent upon the continuing ability of issuers
    of the Bonds or the insurers thereof to meet their obligations.  There can
    be no assurance that the Trust's investment objectives will be achieved. 
    Investment in the Trust should be made with an understanding of the risks
    which an investment in long-term fixed rate debt obligations may entail,
    including the risk that the value of the underlying portfolio will decline
    with increases in interest rates, and that the value of Zero Coupon Bonds
    is subject to greater fluctuation than coupon bonds in response to changes
    in interest rates.  Each Unit in the Trust represents a 1/1990th undivided
    interest in the principal and net income of the Trust.  The principal
    amount of Bonds deposited in the Trust per Unit is reflected in the
    Summary of Essential Information.  (See "Organization" in Part B of this
    Prospectus.)  The Units being offered hereby are issued and outstanding
    Units which have been purchased by the Sponsor in the secondary market. 

          INSURANCE.  Each of the Bonds in the Trust is insured by a municipal
    bond guaranty insurance policy obtained by either the Sponsor ("Sponsor-
    Insured Bonds") or the issuers of the Bonds ("Pre-Insured Bonds") and
    issued by one of the insurance companies (the "Insurance Companies"),
    described under "Insurance on the Bonds" in Part B of this Prospectus,
    covering scheduled payment of principal thereof and interest thereon when
    such amounts shall become due for payment but shall not have been paid by
    the issuer or any other insurer thereof.  The insurance, unless obtained
    by Municipal Bond Investors Assurance Corporation ("MBIA Corp."), will
    also cover any accelerated payments of principal and the increase in
    interest payments or premiums, if any, payable upon mandatory redemption
    of the Bonds if interest on any Bonds is ultimately deemed to be subject
    to regular federal income tax.  Insurance obtained from MBIA Corp. only
    guarantees the accelerated payments required to be made by or on behalf of
    an issuer of small industrial revenue bonds and pollution control bonds if
    there is an event which results in the loss of tax-exempt status of the
    interest on such Bonds, including principal, interest or premium payments,
    if any, as and when required.  To the extent, therefore, that Bonds are
    only covered by insurance obtained from MBIA Corp., such Bonds will not be
    covered for the accelerated payments required to be made by or on behalf
    of an issuer of other than small industrial revenue bonds or pollution
    control revenue bonds if there occurs an event which results in the loss
    of tax-exempt status of the interest on such Bonds.  None of the insurance
    will cover accelerated payments of principal or penalty interest or
    premiums unrelated to taxability of interest on the Bonds (although the
    insurance, including insurance obtained by MBIA Corp., does guarantee
    payment of principal and interest in such amounts and at such times as
    such amounts would have been due absent such acceleration).  The insurance
    relates only to the prompt payment of principal of and interest on the
    securities in the portfolio, and does not remove market risks or guarantee
    the market value of the Units in the Trust.  The terms of the insurance
    are more fully described under "Insurance on the Bonds" in Part B of this
    Prospectus.  For a discussion of the effect of an occurrence of nonpayment
    of principal or interest on any Bonds in the Trust, see "Portfolio
    Supervision" in Part B of this Prospectus.  No representation is made
    herein as to any Bond insurer's ability to meet its obligations under a
    policy of insurance relating to any of the Bonds.  In addition, investors
    should be aware that, subsequent to the Date of Deposit, the rating of the
    claims paying ability of the insurer of an underlying Bond may be
    downgraded, which may result in a downgrading of the rating of the Units
    in the Trust.  The approximate percentage of the aggregate principal
    amount of the portfolio that is insured by each insurance company is as
    follows:  AMBAC Indemnity Corp. ("AMBAC"), 19.4%; Bond Investor's Guaranty
    ("BIG"), 17.6%; Financial Guaranty Insurance Company ("Financial
    Guaranty"), 19.7%; Firemen's Fund Insurance ("Firemen's"), 11.8%; and
    Municipal Bond Insurance Association ("MBIA, Inc."), 31.5%. 

          PUBLIC OFFERING PRICE.  The secondary market Public Offering Price
    of each Unit is equal to the aggregate bid price of the Bonds in the Trust
    divided by the number of Units outstanding, plus a sales charge of 4.9% of
    the Public Offering Price, or 5.152% of the net amount invested in Bonds
    per Unit.  In addition, accrued interest to the expected date of
    settlement is added to the Public Offering Price.  If Units had been
    purchased on the Evaluation Date, the Public Offering Price per Unit would
    have been $920.48 plus accrued interest of $13.63 under the monthly
    distribution plan, $19.01 under the semi-annual distribution plan and
    $19.01 under the annual distribution plan, for a total of $934.11, $939.49
    and $939.49, respectively.  The Public Offering Price per Unit can vary on
    a daily basis in accordance with fluctuations in the aggregate bid price
    of the Bonds.  (See "Public Offering--Offering Price" in Part B of this
    Prospectus.)

          ESTIMATED LONG TERM RETURN AND ESTIMATED CURRENT RETURN.  The rate
    of return on an investment in Units of the Trust is measured in terms of
    "Estimated Current Return" and "Estimated Long Term Return".

          Estimated Long Term Return is calculated by:  (1) computing the
    yield to maturity or to an earlier call date (whichever results in a lower
    yield) for each Bond in the Trust's portfolio in accordance with accepted
    bond practices, which practices take into account not only the interest
    payable on the Bond but also the amortization of premiums or accretion of
    discounts, if any; (2) calculating the average of the yields for the Bonds
    in the Trust's portfolio by weighing each Bond's yield by the market value
    of the Bond and by the amount of time remaining to the date to which the
    Bond is priced (thus creating an average yield for the portfolio of the
    Trust); and (3) reducing the average yield for the portfolio of the Trust
    in order to reflect estimated fees and expenses of the Trust and the
    maximum sales charge paid by investors.  The resulting Estimated Long Term
    Return represents a measure of the return to investors earned over the
    estimated life of the Trust.  (For the Estimated Long Term Return to
    Certificateholders under the monthly, semi-annual and annual distribution
    plans, see "Summary of Essential Information".)

          Estimated Current Return is a measure of the Trust's cash flow. 
    Estimated Current Return is computed by dividing the Estimated Net Annual
    Interest Income per Unit by the Public Offering Price per Unit.  In
    contrast to the Estimated Long Term Return, the Estimated Current Return
    does not take into account the amortization of premium or accretion of
    discount, if any, on the Bonds in the portfolio of the Trust.  Moreover,
    because interest rates on Bonds purchased at a premium are generally
    higher than current interest rates on newly issued bonds of a similar type
    with comparable rating, the Estimated Current Return per Unit may be
    affected adversely if such Bonds are redeemed prior to their maturity.  

          The Estimated Net Annual Interest Income per Unit of the Trust will
    vary with changes in the fees and expenses of the Trustee and the
    Evaluator applicable to the Trust and with the redemption, maturity, sale
    or other disposition of the Bonds in the Trust.  The Public Offering Price
    will vary with the changes in the bid prices of the Bonds.  Therefore,
    there is no assurance that the present Estimated Current Return or
    Estimated Long Term Return will be realized in the future.  (For the
    Estimated Current Return to Certificateholders under the monthly, semi-
    annual and annual distribution plans, see "Summary of Essential
    Information".  See "Estimated Long Term Return and Estimated Current
    Return" in Part B of this Prospectus.)

          A schedule of cash flow projections is available from the Sponsor
    upon request. 

          DISTRIBUTIONS.  Distributions of interest income, less expenses,
    will be made by the Trust either monthly, semi-annually or annually
    depending upon the plan of distribution applicable to the Unit purchased. 
    A purchaser of a Unit in the secondary market will initially receive
    distributions in accordance with the distribution plan chosen by the prior
    owner of such Unit and may thereafter change the plan as provided under
    "Interest and Principal Distributions" in Part B of the Prospectus. 
    Distributions of principal, if any, will be made semi-annually on June 15
    and December 15 of each year.  (See "Rights of Certificateholders--
    Interest and Principal Distributions" in Part B of this Prospectus.  For
    estimated monthly, semi-annual and annual interest distributions, see
    "Summary of Essential Information.")

          MARKET FOR UNITS.  The Sponsor, although not obligated to do so,
    presently maintains and intends to continue to maintain a secondary market
    for the Units at prices based on the aggregate bid price of the Bonds in
    the Trust portfolio.  The reoffer price will be based on the aggregate bid
    price of the Bonds plus a sales charge of 4.9% of the Public Offering
    Price (5.152% of the net amount invested), plus net accrued interest.  If
    a market is not maintained a Certificateholder will be able to redeem his
    Units with the Trustee at a price also based on the aggregate bid price of
    the Bonds.  (See "Liquidity--Sponsor Repurchase" and "Public Offering--
    Offering Price" in Part B of this Prospectus.)
        
          TOTAL REINVESTMENT PLAN.  Certificateholders under the semi-annual
    and annual plans of distribution have the opportunity to have all their
    regular interest distributions, and principal distributions, if any,
    reinvested in available series of "Insured Municipal Securities Trust" or
    "Municipal Securities Trust."  (See "Total Reinvestment Plan" in Part B of
    this Prospectus.  Residents of Texas, see "Total Reinvestment Plan for
    Texas Residents" in Part B of this Prospectus.)  The Plan is not designed
    to be a complete investment program. 


    <PAGE>
       
                        INSURED MUNICIPAL SECURITIES TRUST 
                                     SERIES 6

             SUMMARY OF ESSENTIAL INFORMATION AS OF DECEMBER 31, 1993

    Date of Deposit:  January 30, 1986         Minimum Principal Distribution:
    Principal Amount of Bonds ...$1,700,000     $1.00 per Unit.
    Number of Units .............1,990         Weighted Average Life to
    Fractional Undivided Inter-                Maturity:
      est in Trust per Unit .....1/1990         5.6 Years.
    Principal Amount of                        Minimum Value of Trust:
      Bonds per Unit ............$854.27        Trust may be terminated if
    Secondary Market Public                     value of Trust is less than
      Offering Price**
      Aggregate Bid Price                       $800,000 in principal amount of
        of Bonds in Trust .......$1,742,000+++  Bonds.
      Divided by 1,990 Units ....$875.38       Mandatory Termination Date:
      Plus Sales Charge of 4.9%                 The earlier of December 31,
        of Public Offering Price $45.10         2035 or the disposition of the
      Public Offering Price                     last Bond in the Trust.
        per Unit ................$920.48+      Trustee***:  United States Trust 
    Redemption and Sponsor's                    Company of New York.
      Repurchase Price                         Trustee's Annual Fee:  Monthly 
      per Unit ..................$875.38+       plan $1.03 per $1,000; semi-
                                        +++     annual plan $.55 per $1,000;
                                        ++++    and annual plan is $.36 per
    Excess of Secondary Market                  $1,000.
      Public Offering Price                    Evaluator:  Kenny S&P Evaluation
      over Redemption and                       Services. 
      Sponsor's Repurchase                     Evaluator's Fee for Each
      Price per Unit ............$45.10++++     Evaluation:  Minimum of $12
    Difference between Public                   plus $.25 per each issue of
      Offering Price per Unit                   Bonds in excess of 50 issues
      and Principal Amount per                  (treating separate maturities
      Unit Premium/(Discount) ...$66.21         as separate issues).
    Evaluation Time:  4:00 p.m.                Sponsor:  Bear, Stearns & Co.
      New York Time.                           Inc.
                                               Sponsor's Annual Fee:  Maximum of
                                                $.15 per $1,000 principal
                                                amount of Bonds (see "Trust
                                                Expenses and Charges" in Part B
                                                of this Prospectus).


        PER UNIT INFORMATION BASED UPON INTEREST DISTRIBUTION PLAN ELECTED

                                            Monthly   Semi-Annual   Annual
                                            Option      Option      Option


    Gross annual interest income# .........$69.82       $69.82     $69.82
    Less estimated annual fees and
      expenses ............................  2.16         1.59       1.40
    Estimated net annual interest          ______       ______     ______
      income (cash)# ......................$67.66       $68.23     $68.42
    Estimated interest distribution# ......  5.63        34.11      68.42
    Estimated daily interest accrual# ..... .1879        .1895      .1900
    Estimated current return#++ ........... 7.35%        7.41%      7.43%
    Estimated long term return++ .......... 2.92%        2.99%      3.01%
    Record dates .......................... 1st of     Dec. 1 and   Dec. 1
                                            each month June 1
    Interest distribution dates ........... 15th of    Dec. 15 and  Dec. 15
                                            each month June 15
        
    <PAGE>
       *  The Date of Deposit is the date on which the Trust Agreement was
          signed and the deposit of the Bonds with the Trustee made. 

      **  For information regarding offering price per Unit and applicable
          sales charge under the Total Reinvestment Plan, see "Total
          Reinvestment Plan" in Part B of this Prospectus. 

     ***  The Trustee maintains its corporate trust office at 770 Broadway,
          New York, New York 10003 (tel. no.:  1-800-428-8890).  For
          information regarding redemption by the Trustee, see "Trustee
          Redemption" in Part B of this Prospectus.
       
       +  Plus accrued interest to the expected date of settlement
          (approximately five business days after purchase) of $13.63 monthly,
          $19.01 semi-annually and $19.01 annually. 
        
      ++  The estimated current return and estimated long term return are
          increased for transactions entitled to a discount (see "Employee
          Discounts" in Part B of this Prospectus), and are higher under the
          semi-annual and annual options due to lower Trustee's fees and
          expenses.

     +++  Based solely upon the bid side evaluation of the underlying Bonds
          (including, where applicable, undistributed cash from the principal
          account).  Upon tender for redemption, the price to be paid will be
          calculated as described under "Trustee Redemption" in Part B of this
          Prospectus. 

    ++++  See "Comparison of Public Offering Price, Sponsor's Repurchase Price
          and Redemption Price" in Part B of this Prospectus. 

       #  Does not include income accrual from original issue discount bonds,
          if any.


    <PAGE>
       
                          INFORMATION REGARDING THE TRUST
                              AS OF DECEMBER 31, 1993


    DESCRIPTION OF PORTFOLIO*

          The portfolio of the Trust consists of 14 issues representing
    obligations of issuers located in 12 states.  The Sponsor has not
    participated as a sole underwriter or manager, co-manager or member of an
    underwriting syndicate from which any of the initial aggregate principal
    amount of the Bonds were acquired.  Approximately 7.1% of the Bonds are
    obligations of state and local housing authorities; approximately 25.3%
    are hospital revenue bonds; approximately 14.7% were issued in connection
    with the financing of nuclear generating facilities; and approximately
    1.5% are "mortgage subsidy" bonds.  All of the Bonds in the Trust are
    subject to redemption prior to their stated maturity dates pursuant to
    sinking fund or optional call provisions.  The Bonds may also be subject
    to other calls, which may be permitted or required by events which cannot
    be predicted (such as destruction, condemnation, termination of a
    contract, or receipt of excess or unanticipated revenues).  None of the
    Bonds are general obligation bonds.  Fourteen issues representing
    $1,700,000 of the principal amount of the Bonds are payable from the
    income of a specific project or authority and are not supported by the
    issuer's power to levy taxes.  The portfolio is divided for purpose of
    issue as follows:  Coal Power 2, Federally Insured Mortgage 1, Hospital 4,
    Housing 1, Industrial Development 1, Nuclear Power 2, Pollution Control 1,
    Waste Water 1, and Water and Sewer 1.  For an explanation of the
    significance of these factors see "The Trust--Portfolio" in Part B of this
    Prospectus.

    *     Changes in the Trust Portfolio:  From January 1, 1994 to March 24,
          1994, the entire principal amount of the Bonds in portfolio no. 14
          has been called and is no longer contained in the Trust.  5 Units
          have been redeemed from the Trust.

    <PAGE>

          As of December 31, 1993, $120,000 (approximately 7.1% of the
    aggregate principal amount of the Bonds) were original issue discount
    bonds.  Of these original issue discount bonds, $120,000 (approximately
    7.1% of the aggregate principal amount of the Bonds) were Zero Coupon
    Bonds.  Zero Coupon Bonds do not provide for the payment of any current
    interest and provide for payment at maturity at par value unless sooner
    sold or redeemed.  The market value of Zero Coupon Bonds is subject to
    greater fluctuations than coupon bonds in response to changes in interest
    rates.  Approximately 16.2% of the aggregate principal amount of the Bonds
    in the Trust were purchased at a "market" discount from par value at
    maturity, approximately 76.7% were purchased at a premium and none were
    purchased at par.  For an explanation of the significance of these factors
    see "Discount and Zero Coupon Bonds" in Part B of this Prospectus.  All of
    the Bonds are subject to redemption prior to maturity pursuant to sinking
    fund or call provisions. 

          None of the Bonds in the Trust are subject to the federal individual
    alternative minimum tax under the Tax Reform Act of 1986.  See "Tax
    Status" in Part B of this Prospectus. 

    <PAGE>
                       FINANCIAL AND STATISTICAL INFORMATION


    Selected data for each Unit outstanding for the periods listed below:

                                                                    Distribu-
                                                                    tions of
                                          Distributions of Interest Principal
                                          During the Period (per Unit)  During
                               Net Asset *           Semi-             the
                    Units Out-   Value    Monthly   Annual  Annual  Period
    Period Ended     standing  Per Unit   Option    Option  Option (Per Unit)
    
    
   

    December 31, 1991  2,000   $929.54    $69.96   $70.55   $70.74$  7.50
    December 31, 1992  2,000    911.20     69.12    69.73    69.93  10.00
    December 31, 1993  1,990    891.56     68.22    68.85    69.05   8.07
        
    *     Net Asset Value per Unit is calculated by dividing net assets as
          disclosed in the "Statement of Net Assets" by the number of Units
          outstanding as of the date of the Statement of Net Assets.  See
          Note 5 of Notes to Financial Statements for a description of the
          components of Net Assets.

    <PAGE>

Independent Auditors' Report


The Sponsor, Trustee and Certificateholders
Insured Municipal Securities Trust, Series 6:


We have audited the accompanying statement of net assets, including the
portfolio, of Insured Municipal Securities Trust, Series 6 as of December
31, 1993, and the related statements of operations, and changes in net
assets for each of the years in the three year period then ended.  These
financial statements are the responsibility of the Trustee (see note 2).
Our responsibility is to express an opinion on these financial statements
based on our audits.

We conducted our audits in accordance with generally accepted auditing
standards.  Those standards require that we plan and perform the audit to
obtain reasonable assurance about whether the financial statements are
free of material misstatement.  An audit includes examining, on a test
basis, evidence supporting the amounts and disclosures in the financial
statements.  Our procedures included confirmation of securities owned
as of December 31, 1993, by correspondence with the Trustee.  An audit
also includes assessing the accounting principles used and significant
estimates made by management, as well as evaluating the overall financial
statement presentation.  We believe that our audits provide a reasonable
basis for our opinion.

In our opinion, the financial statements referred to above present
fairly, in all material respects, the financial position of Insured
Municipal Securities Trust, Series 6 as of December 31, 1993, and the
results of its operations and the changes in its net assets for each of
the years in the three year period then ended in conformity with generally
accepted accounting principles.




    KPMG Peat Marwick


New York, New York
March 31, 1994
<PAGE>

                                 Statement of Net Assets
                                                   
                                    December 31, 1993



       Investments in marketable securities,
          at market value (cost  $1,675,823)               $ 1,741,993
                                         
       Excess of other assets over total liabilities            32,213
                                                            ----------

       Net assets (  1,990 units of fractional undivided
          interest outstanding,  $891.56 per  unit)        $ 1,774,206
                                                            ==========

       See accompanying notes to financial statements.
<PAGE>

<TABLE>

                              Statements of Operations
<CAPTION>
                                                           Years ended December 31,  
                                                    --------       ---------      ---------
                                                      1993           1992           1991
                                                    --------       ---------      ---------
<S>                                              <C>               <C>            <C>
     Investment income - interest                $  140,782         143,273        144,510
                                                    --------       ---------      ---------
                    
     Expenses:      
        Trustee's fees                                2,975           2,876          2,652
        Evaluator's fees                                890             823            693
        Sponsor's advisory fee                          259             262            264
                                                    --------       ---------      ---------
                    
                   Total expenses                     4,124           3,961          3,609
                                                    --------       ---------      ---------
                    
                   Investment income, net           136,658         139,312        140,901
                                                    --------       ---------      ---------
                    
     Realized and unrealized gain
       (loss) on investments: 
          Net realized loss on
            bonds sold or called                     (1,500)         (1,200)          (900)
          Unrealized appreciation
           (depreciation) for the year              (21,684)        (16,114)        47,565
                                                    --------       ---------      ---------
                    
                Net gain (loss)
                  on investments                    (23,184)        (17,314)        46,665
                                                    --------       ---------      ---------
                    
                Net increase in net                                                  
                  assets resulting                                                   
                  from operations                $  113,474         121,998        187,566
                                                    ========       =========      =========

     See accompanying notes to financial statements.                                 
</TABLE>

<PAGE>

<TABLE>
                         Statements of Changes in Net Assets
                              
<CAPTION>
                                                           Years ended December 31,  
                                                    --------       ---------      ---------
                                                      1993           1992           1991
                                                    --------       ---------      ---------
<S>                                              <C>               <C>            <C>

    Operations:         
       Investment income, net                     $    136,658      139,312          140,901
       Net realized loss on
         bonds sold or called                          (1,500)       (1,200)            (900)
       Unrealized appreciation
        (depreciation) for the year                   (21,684)      (16,114)          47,565
                                                   -----------     ---------      -----------
                        
                    Net increase in net                                                  
                      assets resulting                                                   
                      from operations                 113,474       121,998          187,566
                                                   -----------     ---------      -----------
                      
    Distributions to Certificateholders:                                               
         Investment income                            136,499       138,680          140,084
         Principal                                     16,059        20,000           15,000
                      
    Redemptions:      
         Interest                                         172        -                 -
         Principal                                      8,934        -                 -
                                                   -----------     ---------      -----------
                      
      Total distributions and redemptions             161,664       158,680          155,084
                                                   -----------     ---------      -----------
                      
                    Total increase (decrease)         (48,190)      (36,682)          32,482
                      
    Net assets at beginning of year                 1,822,396     1,859,078        1,826,596
                                                   -----------   -----------      -----------
                      
    Net assets at end of year (including                                               
       undistributed net investment
       income of  $34,523,   $34,536 and                                               
       $33,904 respectively)                    $  1,774,206     1,822,396        1,859,078
                                                  ===========    ==========      ===========

    See accompanying notes to financial statements.
</TABLE>


<PAGE>

INSURED MUNICIPAL SECURITIES TRUST, SERIES 6

Notes to Financial Statements

December 31, 1993, 1992 and 1991

(1)    Organization

Insured Municipal Securities Trust, Series 6 (Trust) was organized on
January 30, 1986 by Bear, Stearns & Co. Inc. (Sponsor) under the laws
of the State of New York by a Trust Indenture and Agreement, and is
registered under the Investment Company Act of 1940.

(2)    Summary of Significant Accounting Policies

United States Trust Company of New York (Trustee) has custody of and
responsibility for the accounting records and financial statements of
the Trust and is responsible for establishing and maintaining a
system of internal control related thereto.

The Trustee is also responsible for all estimates of expenses and
accruals reflected in the Trust's financial statements.  The
accompanying financial statements have been adjusted to record the
unrealized appreciation (depreciation) of investments and to record
interest income and expenses on the accrual basis.

The discount on the zero-coupon bonds is accreted by the interest
method over the respective lives of the bonds.  The accretion of such
discount is included in interest income; however, it is not
distributed until realized in cash upon maturity or sale of the
respective bonds.

Investments are carried at market value which is determined by either
Standard & Poor's Corporation or Moody's Investors Service, Inc.
(Evaluator) as discussed in Footnotes to Portfolio.  The market value
of the investments is based upon the bid prices for the bonds at the
end of the period, except that the market value on the date of
deposit represents the cost to the Trust based on the offering prices
for investments at that date.  The difference between cost (including
accumulated accretion of original issue discount on zero-coupon
bonds) and market value is reflected as unrealized appreciation
(depreciation) of investments.  Securities transactions are recorded
on the trade date.  Realized gains (losses) from securities
transactions are determined on the basis of average cost of the
securities sold or redeemed.

(3)    Income Taxes

The Trust is not subject to Federal income taxes as provided for by
the Internal Revenue Code.

(4)    Trust Administration

The fees and expenses of the Trust are incurred and paid on the basis
set forth under "Trust Expenses and Charges" in Part B of this
Prospectus.

The Trust Indenture and Agreement provides for interest distributions
as often as monthly (depending upon the distribution plan elected by
the Certificateholders).

The Trust Indenture and Agreement further requires that principal
received from the disposition of bonds, other than those bonds sold
in connection with the redemption of units, be distributed to
Certificateholders.

See "Financial and Statistical Information" in Part A of this
Prospectus for the amounts of per unit distributions during the years
ended December 31, 1993, 1992, and 1991.

The Trust Indenture and Agreement also requires the Trust to redeem
units tendered.  10 units were redeemed during the year ended
December 31, 1993.  No units were redeemed by the Trust during the
years ended December 31, 1992 and 1991.

(5)    Net Assets

      At December 31, 1993, the net assets of the Trust represented the
      interest  of Certificateholders as follows:

   Original cost to Certificateholders                $ 2,098,306
   Less initial gross underwriting commission           (102,800)
                                                        1,995,506

   Cost of securities sold or called                     (322,000)
   Net unrealized appreciation                             66,170
   Undistributed net investment income                     34,523
   Undistributed proceeds from bonds
   sold or called                                               7

       Total                                          $ 1,774,206


    The original cost to Certificateholders, less the initial gross
underwriting commission, represents the aggregate initial public
offering price net of the applicable sales charge on 2,000 units of
fractional  undivided interest of the Trust as of the date of
deposit.

Undistributed net investment income includes accumulated accretion of
original issue discount of $2,317.
<PAGE>

<TABLE>


INSURED MUNICIPAL SECURITIES TRUST, SERIES 6

Portfolio
 December 31, 1993

<CAPTION>

Port-  Aggregate                                  Coupon Rate/   Redemption Feature             
foliO  Principal      Name of Issuer     Ratings  Date(s) of     S.F.--Sinking Fund          Market
No.     Amount      and Title of Bonds     (1)    Maturity(2)    Ref.--Refunding (2) (7)    Value(3)
- --     ---------   ---------------------   ----   ------------   ----------------------     ---------
<S>   <C>          <C>                     <C>    <C>            <C>                       <C>
1     $  180,000   Moffat County,          AAA    6.125%         1/01/97 @ 100 S.F.        $  180,396
                   Colorado Pollution             1/01/2007      2/01/94 @ 100 Ref.             
                   Control Revenue
                   Bonds, Tri-State
                   Generation  
                   Transmission
                   Association (AMBAC)   
                               
                               
2        130,000   The Hospital            AAA    9.250          10/01/06 @ S.F.              145,921
                   Authority of Walker,           10/01/2010     10/01/95 @ 102 Ref.            
                   Dade and Catoosa
                   Counties (Georgia)
                   Refunding Revenue
                   Anticipation
                   Certificates, 1985
                   Series  (Financial
                   Guaranty) (5)
                               
                               
3         20,000   County of Cook,         AAA    9.300          6/01/00 @ 100 S.F.            21,929
                   Illinois Single                6/01/2009      6/01/96 @ 102 Ref.             
                   Family Mortgage
                   Revenue Bonds, 1985   
                   Series A (MBIA)
                               
                               
4        100,000   Hospital Authority of   AAA    9.250          11/01/06 @ 100 S.F.          112,722
                   St. Joseph County              11/1/2015      11/01/95 @ 102 Ref.            
                   (Indiana) Insured
                   Hospital Revenue
                   Bonds, 1985 Series
                   (Memorial Hospital of 
                   South Bend Project)   
                   (MBIA) (5)  
                               
                               
5        200,000   Southern Minnesota,     AAA    9.500          No Sinking Fund              227,262
                   Municipal Power                1/01/2017      1/01/96 @ 102 Ref.             
                   Agency Power Supply   
                   System Revenue Bonds, 
                   1985 Series A (BIG)   
                   (5)         
                               
                               
6        105,000   Ocean County            AAA    8.700          1/01/07 @ 100 S.F.           117,677
                   Utilities Authority            1/01/2011      1/01/96 @ 102 Ref.             
                   New Jersey Waste
                   Water Revenue
                   Refunding Bonds 1985  
                   Series (Financial
                   Guaranty) (5)
                               
7        200,000   Albuquerque, New        AA-    9.375          12/01/96 @ 100 S.F.          215,552
                   Mexico Industrial              12/01/2005     12/01/94 @ 102 Ref.            
                   Development Bonds for 
                   Capital Glass and
                   Aluminum Corporation  
                   1985 Series 
                   (Firemen's Fund
                   Insurance)  
                               
                               
8        100,000   City of Farmington,     AAA    9.750          5/15/06 @ 100 S.F.           116,268
                   New Mexico Utility             5/15/2013      5/15/96 @ 102 Ref.             
                   System Revenue Bonds  
                   1985 Series 
                   (Financial Guaranty)  
                   (5)         
                               
9        150,000   Piedmont Municipal      AAA    9.250          1/01/16 @ 100 S.F.           171,129
                   Power Agency (South            1/01/2019      1/01/96 @ 103 Ref.             
                   Carolina) Electric
                   Revenue Bonds, 1985   
                   Series (AMBAC) (5)
                               
                               
 10    100,000     Texas (Harris County)          3/15/2002      3/15/95 @ 100 Ref.          107,596
                   Waterworks and Sewer  
                   System Revenue Bonds  
                   1985 Series (BIG) (5) 
                               
11     100,000     Facilities                     9/01/2014      9/01/95 @ 102 Ref.           111,604
                   Development 
                   Corporation Hospital  
                   Refunding Revenue
                   Bonds, 1985 Series
                   (Hillcrest Baptist
                   Medical Center
                   Project) (MBIA) (5)   
                               
12       95,000    Agency (a political            7/01/2014      7/01/95 @ 100 Ref.            99,712
                   subdivision of the
                   State of Utah) Power  
                   Supply System Revenue 
                   Refunding Bonds 1985  
                   Series J (MBIA) (5)   
                               
                               
13       100,000   Wisconsin Health        AAA    9.250          7/01/06 @ 100 S.F.           110,134
                   Facility Authority             7/01/2012      7/01/95 @ 102 Ref.             
                   Hospital Revenue
                   Bonds, Sisters
                   Services Incorporated 
                   - St. Mary's Hospital 
                   1985 Series(MBIA)
                               
                        See    
14       120,000   Maryland Economic              6/01/2027      1/06/94   @ 3.409 Ref.        4,091
                   Development Revenue   
                   Bonds, 1985 Series
                   (FHA Insured Mortgage 
                   Loan - The Regency
                   Club II Facility)
                   (MBIA) (5)  
       ---------                                                                            ---------
    $  1,700,000                                                                         $  1,741,993
       =========                                                                            =========

See accompanying footnotes to portfolio and notes to financial statements.                      
</TABLE>

<PAGE>
                              
INSURED MUNICIPAL SECURITIES TRUST, SERIES 6

Footnotes to Portfolio

December 31, 1993

(1) All ratings are by Standard & Poor's Corporation.  A brief description
of the ratings symbols and their meanings is set forth under
"Description of Bond Ratings" in Part B of this Prospectus.

(2) See "The Trust - Portfolio" in Part B of this Prospectus for an
explanation of redemption features.  See "Tax Status" in Part B of
this Prospectus for a statement of the Federal tax consequences to a
Certificateholder upon the sale, redemption or maturity of a bond.

(3) At December 31, 1993, the net unrealized appreciation of all the 
bonds was comprised of the following:

        Gross unrealized appreciation                     $ 72,885
        Gross unrealized depreciation                       (6,715)

        Net unrealized appreciation                       $ 66,170

(4)  The annual interest income, based upon bonds held at December 31, 
1993, (excluding accretion of original issue discount on zero-coupon 
bonds) to the Trust is $138,945.

(5)  The bonds have been prerefunded and will be redeemed at the next
refunding call date.

(6)  Bonds sold or called after December 31, 1993 are noted in a footnote
"Changes in Trust Portfolio" under "Description of Portfolio" in Part
A of this Prospectus.

(7)  The Bonds may also be subject to other calls, which may be permitted 
or required by events which cannot be predicted (such as destruction,
condemnation, termination of a contract, or receipt of excess or
unanticipated revenues).
<PAGE>


                 NOTE:  Part A of This Prospectus May Not Be     
                        Distributed Unless Accompanied by Part B.


                        INSURED MUNICIPAL SECURITIES TRUST

                               18TH DISCOUNT SERIES
                              (MULTIPLIER PORTFOLIO)


                                                                              
       
          The Trust is a unit investment trust designated 18th Discount Series
    ("Insured Municipal Discount Trust") with an underlying portfolio of long-
    term insured tax-exempt bonds issued by or on behalf of states,
    municipalities and public authorities and was formed to preserve capital
    and to provide interest income (including, where applicable, earned
    original issue discount) which, in the opinions of bond counsel to the
    respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law but may be subject to state
    and local taxes.  Capital gains are subject to tax.  (See "Tax Status" and
    "The Trust--Portfolio" in Part B of this Prospectus.)  The Sponsor is
    Bear, Stearns & Co. Inc.  The value of the Units of the Trust will
    fluctuate with the value of the underlying bonds.  Minimum purchase:  1
    Unit. 

                                                                              


          This Prospectus consists of two parts.  Part A contains the Summary
    of Essential Information as of December 31, 1993 (the "Evaluation Date"),
    a summary of certain specific information regarding the Trust and audited
    financial statements of the Trust, including the related portfolio, as of
    the Evaluation Date.  Part B of this Prospectus contains a general summary
    of the Trust. 
        
                    Investors should retain both parts of this
                         Prospectus for future reference. 

                                                                              


     THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES
     AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE
     COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR
     ADEQUACY OF THIS PROSPECTUS.  ANY REPRESENTATION TO THE CONTRARY IS A
     CRIMINAL OFFENSE.

       
                      Prospectus Part A Dated April 29, 1994
        
     

    <PAGE>
       
          THE TRUST.  The Trust is a unit investment trust formed to preserve
    capital and to provide interest income (including, where applicable,
    earned original issue discount) which, in the opinions of bond counsel to
    the respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law through investment in a
    fixed, diversified portfolio of long-term insured bonds (the "Bonds")
    issued by or on behalf of states, municipalities and public authorities
    which, because of irrevocable insurance, are rated "AAA" by Standard &
    Poor's Corporation.  Although the Supreme Court has determined that
    Congress has the authority to subject interest on bonds such as the Bonds
    in the Trust to regular federal income taxation, existing law excludes
    such interest from regular federal income tax.  Such interest income may,
    however, be subject to the federal corporate alternative minimum tax and
    to state and local taxes.  (See "Tax Status" in Part B of this
    Prospectus.)  For a list of ratings on the Evaluation Date, see
    "Portfolio."  The Bonds were acquired at prices which resulted in the
    portfolio as a whole being purchased at a deep discount from par value. 
    The portfolio may also include bonds issued at an original issue discount. 
    Additionally, some of the Bonds in the portfolio may be "Zero Coupon
    Bonds," which are original issue discount bonds that provide for payment
    at maturity at par value, but do not provide for the payment of any
    current interest.  Some of the Bonds in the Trust have been issued with
    optional refunding or refinancing provisions ("Refunded Bonds") whereby
    the issuer of the Bond has the right to call such Bond prior to its stated
    maturity date (and other than pursuant to sinking fund provisions) and to
    issue new bonds ("Refunding Bonds") in order to finance the redemption. 
    Issuers typically utilize refunding calls in order to take advantage of
    lower interest rates in the marketplace.  Some of these Refunded Bonds may
    be called for redemption pursuant to pre-refunding provisions ("Pre-
    Refunded Bonds") whereby the proceeds from the issue of the Refunding
    Bonds are typically invested in government securities in escrow for the
    benefit of the holders of the Pre-Refunded Bonds until the refunding call
    date.  Usually, Pre-Refunded Bonds will bear a triple-A rating because of
    this escrow.  The issuers of Pre-Refunded Bonds must call such Bonds on
    their refunding call date.  Therefore, as of such date, the Trust will
    receive the call price for such bonds but will cease receiving interest
    income with respect to them.  For a list of those Bonds which are Pre-
    Refunded Bonds, if any, as of the Evaluation Date, see "Notes to Financial
    Statements" in this Part A.  Some of the Bonds in the portfolio may have
    been purchased at an aggregate premium over par.  All of the Bonds in the
    Trust were rated "AAA" by Standard & Poor's Corporation at the time
    originally deposited in the Trust.  This rating results from insurance
    relating only to the Bonds in the Trust and not to the Units of the Trust. 
    The insurance does not remove market risk, as it does not guarantee the
    market value of the Units.  For a discussion of the significance of such
    ratings, see "Description of Bond Ratings" in Part B of this Prospectus,
    and for a list of ratings on the Evaluation Date see the "Portfolio."  The
    payment of interest and preservation of capital are, of course, dependent
    upon the continuing ability of issuers of the Bonds or the insurers
    thereof to meet their obligations.  There can be no assurance that the
    Trust's investment objectives will be achieved.  Investment in the Trust
    should be made with an understanding of the risks which an investment in
    long-term fixed rate debt obligations may entail, including the risk that
    the value of the underlying portfolio will decline with increases in
    interest rates, and that the value of Zero Coupon Bonds is subject to
    greater fluctuation than coupon bonds in response to changes in interest
    rates.  Each Unit in the Trust represents a 1/10000th undivided interest
    in the principal and net income of the Trust.  The principal amount of
    Bonds deposited in the Trust per Unit is reflected in the Summary of
    Essential Information.  (See "Organization" in Part B of this Prospectus.) 
    The Units being offered hereby are issued and outstanding Units which have
    been purchased by the Sponsor in the secondary market. 

          INSURANCE.  Each of the Bonds in the Trust is insured by a municipal
    bond guaranty insurance policy obtained by either the Sponsor ("Sponsor-
    Insured Bonds") or the issuers of the Bonds ("Pre-Insured Bonds") and
    issued by one of the insurance companies (the "Insurance Companies"),
    described under "Insurance on the Bonds" in Part B of this Prospectus,
    covering scheduled payment of principal thereof and interest thereon when
    such amounts shall become due for payment but shall not have been paid by
    the issuer or any other insurer thereof.  The insurance, unless obtained
    by Municipal Bond Investors Assurance Corporation ("MBIA Corp."), will
    also cover any accelerated payments of principal and the increase in
    interest payments or premiums, if any, payable upon mandatory redemption
    of the Bonds if interest on any Bonds is ultimately deemed to be subject
    to regular federal income tax.  Insurance obtained from MBIA Corp. only
    guarantees the accelerated payments required to be made by or on behalf of
    an issuer of small industrial revenue bonds and pollution control bonds if
    there is an event which results in the loss of tax-exempt status of the
    interest on such Bonds, including principal, interest or premium payments,
    if any, as and when required.  To the extent, therefore, that Bonds are
    only covered by insurance obtained from MBIA Corp., such Bonds will not be
    covered for the accelerated payments required to be made by or on behalf
    of an issuer of other than small industrial revenue bonds or pollution
    control revenue bonds if there occurs an event which results in the loss
    of tax-exempt status of the interest on such Bonds.  None of the insurance
    will cover accelerated payments of principal or penalty interest or
    premiums unrelated to taxability of interest on the Bonds (although the
    insurance, including insurance obtained by MBIA Corp., does guarantee
    payment of principal and interest in such amounts and at such times as
    such amounts would have been due absent such acceleration).  The insurance
    relates only to the prompt payment of principal of and interest on the
    securities in the portfolio, and does not remove market risks or guarantee
    the market value of the Units in the Trust.  The terms of the insurance
    are more fully described under "Insurance on the Bonds" in Part B of this
    Prospectus.  For a discussion of the effect of an occurrence of nonpayment
    of principal or interest on any Bonds in the Trust, see "Portfolio
    Supervision" in Part B of this Prospectus.  No representation is made
    herein as to any Bond insurer's ability to meet its obligations under a
    policy of insurance relating to any of the Bonds.  In addition, investors
    should be aware that, subsequent to the Date of Deposit, the rating of the
    claims-paying ability of the insurer of an underlying Bond may be
    downgraded, which may result in a downgrading of the rating of the Units
    in the Trust.  The approximate percentage of the aggregate principal
    amount of the portfolio that is insured by each Insurance Company is as
    follows:  AMBAC Indemnity Corp. ("AMBAC"), 16.6%; Financial Guaranty
    Insurance Company ("Financial Guaranty"), 19.7%; and Municipal Bond
    Insurance Association ("MBIA"), 63.7%. 

          PUBLIC OFFERING PRICE.  The secondary market Public Offering Price
    of each Unit is equal to the aggregate bid price of the Bonds in the Trust
    divided by the number of Units outstanding, plus a sales charge of 5.5% of
    the Public Offering Price, or 5.820% of the net amount invested in Bonds
    per Unit.  In addition, accrued interest to the expected date of
    settlement, including earned original issue discount, is added to the
    Public Offering Price.  If Units had been purchased on the Evaluation
    Date, the Public Offering Price per Unit would have been $616.77 plus
    accrued interest of $7.57 under the monthly distribution plan, $11.03
    under the semi-annual distribution plan and $11.06 under the annual
    distribution plan, for a total of $624.34, $627.80 and $627.83,
    respectively.  The Public Offering Price per Unit can vary on a daily
    basis in accordance with fluctuations in the aggregate bid price of the
    Bonds.  (See "Public Offering--Offering Price" in Part B of this
    Prospectus.)

          ESTIMATED LONG TERM RETURN AND ESTIMATED CURRENT RETURN.  The rate
    of return on an investment in Units of the Trust is measured in terms of
    "Estimated Current Return" and "Estimated Long Term Return".

          Estimated Long Term Return is calculated by:  (1) computing the
    yield to maturity or to an earlier call date (whichever results in a lower
    yield) for each Bond in the Trust's portfolio in accordance with accepted
    bond practices, which practices take into account not only the interest
    payable on the Bond but also the amortization of premiums or accretion of
    discounts, if any; (2) calculating the average of the yields for the Bonds
    in the Trust's portfolio by weighing each Bond's yield by the market value
    of the Bond and by the amount of time remaining to the date to which the
    Bond is priced (thus creating an average yield for the portfolio of the
    Trust); and (3) reducing the average yield for the portfolio of the Trust
    in order to reflect estimated fees and expenses of the Trust and the
    maximum sales charge paid by investors.  The resulting Estimated Long Term
    Return represents a measure of the return to investors earned over the
    estimated life of the Trust.  (For the Estimated Long Term Return to
    Certificateholders under the monthly, semi-annual and annual distribution
    plans, see "Summary of Essential Information".)

          Estimated Current Return is a measure of the Trust's cash flow. 
    Estimated Current Return is computed by dividing the Estimated Net Annual
    Interest Income per Unit by the Public Offering Price per Unit.  In
    contrast to the Estimated Long Term Return, the Estimated Current Return
    does not take into account the amortization of premium or accretion of
    discount, if any, on the Bonds in the portfolio of the Trust.  Moreover,
    because interest rates on Bonds purchased at a premium are generally
    higher than current interest rates on newly issued bonds of a similar type
    with comparable rating, the Estimated Current Return per Unit may be
    affected adversely if such Bonds are redeemed prior to their maturity.

          The Estimated Net Annual Interest Income per Unit of the Trust will
    vary with changes in the fees and expenses of the Trustee and the
    Evaluator applicable to the Trust and with the redemption, maturity, sale
    or other disposition of the Bonds in the Trust.  The Public Offering Price
    will vary with changes in the bid prices of the Bonds.  Therefore, there
    is no assurance that the present Estimated Current Return or Estimated
    Long Term Return will be realized in the future.  (For the Estimated
    Current Return to Certificateholders under the monthly, semi-annual and
    annual distribution plans, see "Summary of Essential Information".  See
    "Estimated Long Term Return and Estimated Current Return" in Part B of
    this Prospectus.)

          A schedule of cash flow projections is available from the Sponsor
    upon request.

          DISTRIBUTIONS.  Distributions of interest income, less expenses,
    will be made by the Trust either monthly, semi-annually or annually
    depending upon the plan of distribution applicable to the Unit purchased. 
    A purchaser of a Unit in the secondary market will initially receive
    distributions in accordance with the distribution plan chosen by the prior
    owner of such Unit and may thereafter change the plan as provided under
    "Interest and Principal Distributions" in Part B of this Prospectus. 
    Distributions of principal, if any, will be made semi-annually on June 15
    and December 15 of each year.  (See "Rights of Certificateholders--
    Interest and Principal Distributions" in Part B of this Prospectus.  For
    estimated monthly, semi-annual and annual interest distributions, see
    "Summary of Essential Information.")

          MARKET FOR UNITS.  The Sponsor, although not obligated to do so,
    presently maintains and intends to continue to maintain a secondary market
    for the Units at prices based on the aggregate bid price of the Bonds in
    the Trust portfolio.  The reoffer price will be based on the aggregate bid
    price of the Bonds plus a sales charge of 5.5% of the Public Offering
    Price (5.820% of the net amount invested), plus net accrued interest.  If
    a market is not maintained a Certificateholder will be able to redeem his
    Units with the Trustee at a price also based on the aggregate bid price of
    the Bonds.  (See "Liquidity--Sponsor Repurchase" and "Public Offering--
    Offering Price" in Part B of this Prospectus.)
        
          TOTAL REINVESTMENT PLAN.  Certificateholders under the semi-annual
    and annual plans of distribution have the opportunity to have all their
    regular interest distributions, and principal distributions, if any,
    reinvested in available series of "Insured Municipal Securities Trust" or
    "Municipal Securities Trust."  (See "Total Reinvestment Plan" in Part B of
    this Prospectus.  Residents of Texas see "Total Reinvestment Plan for
    Texas Residents" in Part B of this Prospectus.)  The Plan is not designed
    to be a complete investment program. 


    <PAGE>
       
                        INSURED MUNICIPAL SECURITIES TRUST
                               18TH DISCOUNT SERIES

             SUMMARY OF ESSENTIAL INFORMATION AS OF DECEMBER 31, 1993

    Date of Deposit:  March 26, 1986           Minimum Principal Distribution:
    Principal Amount of Bonds ...$9,910,000     $1.00 per Unit.
    Number of Units .............10,000        Weighted Average Life to
    Fractional Undivided Inter-                Maturity:
      est in Trust per Unit .....1/10000        17.8 Years.
    Principal Amount of                        Minimum Value of Trust:
      Bonds per Unit ............$991.00        Trust may be terminated if
    Secondary Market Public                     value of Trust is less than
      Offering Price**                          $4,000,000 in principal amount
      Aggregate Bid Price                       of Bonds.
        of Bonds in Trust .......$5,828,454+++ Mandatory Termination Date:
      Divided by 10,000 Units ...$582.85        The earlier of December 31,
      Plus Sales Charge of 5.5%                 2035 or the disposition of the
        of Public Offering Price $33.92         last Bond in the Trust.
      Public Offering Price                    Trustee***:  United States Trust 
        per Unit ................$616.77+       Company of New York.
    Redemption and Sponsor's                   Trustee's Annual Fee:  Monthly 
      Repurchase Price                          plan $1.03 per $1,000; semi-
      per Unit ..................$582.85+       annual plan $.55 per $1,000;
                                        +++     and annual plan is $.36 per
                                        ++++    $1,000.
    Excess of Secondary Market                 Evaluator:  Kenny S&P Evaluation
      Public Offering Price                     Services. 
      over Redemption and                      Evaluator's Fee for Each
      Sponsor's Repurchase                      Evaluation:  Minimum of $12
      Price per Unit ............$33.92++++     plus $.25 per each issue of
    Difference between Public                   Bonds in excess of 50 issues
      Offering Price per Unit                   (treating separate maturities
      and Principal Amount per                  as separate issues).
      Unit Premium/(Discount) ...$(374.23)     Sponsor:  Bear, Stearns & Co.
    Evaluation Time:  4:00 p.m.                Inc.
      New York Time.                           Sponsor's Annual Fee:  Maximum of
                                                $.15 per $1,000 principal
                                                amount of Bonds (see "Trust
                                                Expenses and Charges" in Part B
                                                of this Prospectus).

        PER UNIT INFORMATION BASED UPON INTEREST DISTRIBUTION PLAN ELECTED

                                            Monthly   Semi-Annual   Annual
                                            Option      Option      Option

    Gross annual interest income# .........$45.38       $45.38     $45.38
    Less estimated annual fees and
      expenses ............................  1.85         1.20        .99
    Estimated net annual interest          ______       ______     ______
      income (cash)# ......................$43.53       $44.18     $44.39
    Estimated interest distribution# ......  3.62        22.09      44.39
    Estimated daily interest accrual# ..... .1209        .1227      .1233
    Estimated current return#++ ........... 7.06%        7.16%      7.20%
    Estimated long term return++ .......... 3.93%        4.04%      4.07%
    Record dates .......................... 1st of      Dec. 1 and  Dec. 1
                                            each month  June 1
    Interest distribution dates ........... 15th of     Dec. 15 and Dec. 15
                                            each month  June 15
        
    <PAGE>
       *  The Date of Deposit is the date on which the Trust Agreement was
          signed and the deposit of the Bonds with the Trustee made.

      **  For information regarding offering price per Unit and applicable
          sales charge under the Total Reinvestment Plan, see "Total
          Reinvestment Plan" in Part B of this Prospectus. 

     ***  The Trustee maintains its corporate trust office at 770 Broadway,
          New York, New York 10003 (tel. no. 1-800-428-8890).  For information
          regarding redemption by the trustee, see "Trustee Redemption" in
          Part B of this Prospectus.
       
       +  Plus accrued interest to the expected date of settlement
          (approximately five business days after purchase) of $7.57 monthly,
          $11.03 semi-annually and $11.06 annually. 
        
      ++  The estimated current return and estimated long term return are
          increased for transactions entitled to a discount (see "Employee
          Discounts" in Part B of this Prospectus), and are higher under the
          semi-annual and annual options due to lower Trustee's fees and
          expenses.

     +++  Based solely upon the bid side evaluation of the underlying Bonds
          (including, where applicable, undistributed cash from the principal
          account).  Upon tender for redemption, the price to be paid will be
          calculated as described under "Trustee Redemption" in Part B of this
          Prospectus. 

    ++++  See "Comparison of Public Offering Price, Sponsor's Repurchase Price
          and Redemption Price" in Part B of this Prospectus. 

       #  Does not include income accrual from original issue discount bonds,
          if any.

    <PAGE>
       
                          INFORMATION REGARDING THE TRUST
                              AS OF DECEMBER 31, 1993


    DESCRIPTION OF PORTFOLIO*

          The portfolio of the Trust consists of 24 issues representing
    obligations of issuers located in 17 states and the District of Columbia. 
    The Sponsor has not participated as a sole underwriter or manager, co-
    manager or member of an underwriting syndicate from which any of the
    initial aggregate principal amount of the Bonds were acquired. 
    Approximately 49.5% of the Bonds are obligations of state and local
    housing authorities; approximately 13.7% are hospital revenue bonds; none
    were issued in connection with the financing of nuclear generating
    facilities; and none are "mortgage subsidy" bonds.  All of the Bonds in
    the Trust are subject to redemption prior to their stated maturity dates
    pursuant to sinking fund or optional call provisions.  The Bonds may also
    be subject to other calls, which may be permitted or required by events
    which cannot be predicted (such as destruction, condemnation, termination
    of a contract, or receipt of excess or unanticipated revenues).  One issue
    representing $160,000 of the principal amount of the Bonds is a general
    obligation bond.  All 23 of the remaining issues representing $9,750,000
    of the principal amount of the Bonds are payable from the income of a
    specific project or authority and are not supported by the issuer's power
    to levy taxes.  The portfolio is divided for purpose of issue as follows: 
    Airport 2, Coal Power 4, Federally Insured Mortgage 2, Gas 1, Hospital 6,
    Multi-Family Housing 2, Pollution Control 1, Sanitation District 1,
    Sewer 1, Solid Waste 1, Utility District 1 and Water 1.  For an
    explanation of the significance of these factors see "The Trust--
    Portfolio" in Part B of this Prospectus. 


    *     Changes in the Trust Portfolio:  From January 1, 1994 to March 24,
          1994, the entire principal amount of the Bonds in portfolio no. 24
          has been called and is no longer contained in the Trust.  17 Units
          have been redeemed from the Trust.

          As of December 31, 1993, $4,900,000 (approximately 49.5% of the
    aggregate principal amount of the Bonds) were original issue discount
    bonds.  Of these original issue discount bonds, $4,900,000 (approximately
    49.5% of the aggregate principal amount of the Bonds) were Zero Coupon
    Bonds.  Zero Coupon Bonds do not provide for the payment of any current
    interest and provide for payment at maturity at par value unless sooner
    sold or redeemed.  The market value of Zero Coupon Bonds is subject to
    greater fluctuations than coupon bonds in response to changes in interest
    rates.  Approximately 5.9% of the aggregate principal amount of the Bonds
    in the Trust were purchased at a "market" discount from par value at
    maturity, approximately 44.6% were purchased at a premium and none were
    purchased at par.  For an explanation of the significance of these factors
    see "Discount and Zero Coupon Bonds" in Part B of this Prospectus. 

          None of the Bonds in the Trust are subject to the federal individual
    alternative minimum tax under the Tax Reform Act of 1986.  See "Tax
    Status" in Part B of this Prospectus. 

        
    <PAGE>
     
                       FINANCIAL AND STATISTICAL INFORMATION

    Selected data for each Unit outstanding for the periods listed below:
       
                                                                    Distribu-
                                                                    tions of
                                          Distributions of Interest Principal
                                          During the Period (per Unit)  During
                               Net Asset *           Semi-             the
                    Units Out-   Value    Monthly   Annual  Annual  Period
    Period Ended     standing  Per Unit   Option    Option  Option (Per Unit)

    December 31, 1991 10,000   $604.09    $43.56   $44.16   $44.38    -0-
    December 31, 1992 10,000    598.88     43.50    44.16    44.38    -0-
    December 31, 1993 10,000    593.95     43.44    44.16    44.38    -0-


    *     Net Asset Value per Unit is calculated by dividing net assets as
          disclosed in the "Statement of Net Assets" by the number of Units
          outstanding as of the date of the Statement of Net Assets.  See
          Note 5 of Notes to Financial Statements for a description of the
          components of Net Assets.
        
    <PAGE>

Independent Auditors' Report


The Sponsor, Trustee and Certificateholders
Insured Municipal Securities Trust, 18th Discount Series:


We have audited the accompanying statement of net assets, including the
portfolio, of Insured Municipal Securities Trust, 18th Discount Series
as of December 31, 1993, and the related statements of operations, and
changes in net assets for each of the years in the three year period
then ended.  These financial statements are the responsibility of the
Trustee (see note 2).  Our responsibility is to express an opinion on
these financial statements based on our audits.

We conducted our audits in accordance with generally accepted auditing
standards.  Those standards require that we plan and perform the audit to
obtain reasonable assurance about whether the financial statements are
free of material misstatement.  An audit includes examining, on a test
basis, evidence supporting the amounts and disclosures in the financial
statements.  Our procedures included confirmation of securities owned
as of December 31, 1993, by correspondence with the Trustee.  An audit
also includes assessing the accounting principles used and significant
estimates made by management, as well as evaluating the overall financial
statement presentation.  We believe that our audits provide a reasonable
basis for our opinion.

In our opinion, the financial statements referred to above present fairly,
in all material respects, the financial position of Insured Municipal
Securities Trust, 18th Discount Series as of December 31, 1993, and
the results of its operations and the changes in its net assets for
each of the years in the three year period then ended in conformity
with generally accepted accounting principles.




    KPMG Peat Marwick


New York, New York
March 31, 1994

<PAGE>



                              Statement of Net Assets 
            
                                 December 31, 1993    
            
    Investments in marketable securities,          
       at market value (cost     $5,811,300)               $  5,828,454
          
    Excess of other assets over total liabilities               111,056
                                                             ----------
          
    Net assets 10,000 units  of fractional undivided                
       interest outstanding, $593.95 per  unit)            $  5,939,510
                                                             ===========
           
       See accompanying notes to financial statements.               

<PAGE>

<TABLE>
                                         Statements of Operations
<CAPTION>
                                              Years ended December 31,       
                                      ---------- ---  --------- ---  ----------
                                         1993           1992            1991 
                                      ----------      ---------      ----------
<S>                                <C>                <C>            <C>
Investment income - interest       $    472,127        471,626         468,778
                                      ----------      ---------      ----------
                   
Expenses:          
   Trustee's fees                        11,010         10,276           9,335
   Evaluator's fees                       3,557          3,287           2,772
   Sponsor's advisory fee                 1,487          1,487           1,487
                                      ----------      ---------      ----------
                   
           Total expenses                16,054         15,050          13,594
                                      ----------      ---------      ----------
                   
           Investment income, net       456,073        456,576         455,184
                   
Unrealized appreciation            
  (depreciation) for the year           (67,317)       (70,419)        188,731
                                      ----------      ---------      ----------
                   
           Net increase in net     
             assets resulting      
             from operations       $    388,756        386,157         643,915
                                      ==========      =========      ==========

See accompanying notes to financial statements.
</TABLE>

<PAGE>

<TABLE>
                       Statements of Changes in Net Assets
<CAPTION>
                                                           Years ended December 31,         
                                                 -----------  -  ------------ -- -------------
                                                    1993             1992            1991   
                                                 -----------     ------------    -------------
<S>                                           <C>                <C>             <C>
   Operations:                    
      Investment income, net                  $     456,073          456,576          455,184
      Unrealized appreciation     
        (depreciation) for the year                 (67,317)         (70,419)         188,731
                                                 -----------     ------------    -------------
                                  
                  Net increase in net
                    assets resulting
                    from operations                 388,756          386,157          643,915
                                  
   Distributions to Certificateholders of         
        Investment income                           438,008          438,345          438,640
                                                 -----------     ------------    -------------
                                  
                  Total increase (decrease)         (49,252)         (52,188)         205,275
                                  
   Net assets at beginning of year                5,988,762        6,040,950        5,835,675
                                                 -----------     ------------    -------------
                                  
   Net assets at end of year (including           
      undistributed net investment
      income of $214,700,   $196,635 and          
      $178,404 respectively)                  $   5,939,510        5,988,762        6,040,950
                                                 ===========     ============    =============

   See accompanying notes to financial statements.

</TABLE>

<PAGE>

Notes to Financial Statements

December 31, 1993, 1992 and 1991

(1)    Organization

Insured Municipal Securities Trust, 18th Discount Series (Trust) was
organized on March 26, 1986 by Bear, Stearns & Co. Inc. (Sponsor)
under the laws of the State of New York by a Trust Indenture and
Agreement, and is registered under the Investment Company Act
of 1940.

(2)    Summary of Significant Accounting Policies

United States Trust Company of New York (Trustee) has custody of and
responsibility for the accounting records and financial statements of
the Trust and is responsible for establishing and maintaining a
system of internal control related thereto.

The Trustee is also responsible for all estimates of expenses and
accruals reflected in the Trust's financial statements.  The
accompanying financial statements have been adjusted to record the
unrealized appreciation (depreciation) of investments and to record
interest income and expenses on the accrual basis.

The discount on the zero-coupon bonds is accreted by the interest
method over the respective lives of the bonds.  The accretion of such
discount is included in interest income; however, it is not
distributed until realized in cash upon maturity or sale of the
respective bonds.

Investments are carried at market value which is determined by either
Standard and Poor's Corporation or Moody's Investors Service, Inc.
(Evaluator) as discussed in Footnotes to Portfolio.  The market value
of the investments is based upon the bid prices for the bonds at the
end of the year, except that the market value on the date of deposit
represents the cost to the Trust based on the offering prices for
investments at that date.  The difference between cost (including
accumulated accretion of original issue discount on zero-coupon
bonds) and market value is reflected as unrealized appreciation
(depreciation) of investments.  Securities transactions are recorded
on the trade date.  Realized gains (losses) from securities
transactions are determined on the basis of average cost of the
securities sold or redeemed.

(3)    Income Taxes

The Trust is not subject to Federal income taxes as provided for by
the Internal Revenue Code.

(4)    Trust Administration

The fees and expenses of the Trust are incurred and paid on the basis
set forth under "Trust Expenses and Charges" in Part B of this
Prospectus.

The Trust Indenture and Agreement provides for interest distributions
as often as monthly (depending upon the distribution plan elected by
the Certificateholders).

The Trust Indenture and Agreement further requires that principal
received from the disposition of bonds, other than those bonds sold
in connection with the redemption of units, be distributed to
Certificateholders.

See "Financial and Statistical Information" in Part A of this
Prospectus for the amounts of per unit distributions during the years
ended December 31, 1993, 1992, and 1991.

The Trust Indenture and Agreement also requires the Trust to redeem
units tendered.  No units have been redeemed since the inception of
the Trust.

(5)    Net Assets

At December 31, 1993, the net assets of the Trust represented the
interest  of Certificateholders as follows:                
    
  Original cost to Certificateholders                $ 6,143,300
  Less initial gross underwriting commission            (337,900)
                                                       5,805,400

  Cost of securities sold or called                      (97,744)
  Net unrealized appreciation                             17,154
  Undistributed net investment income                    214,700
         
       Total                                           $ 5,939,510


    The original cost to Certificateholders, less the initial gross
underwriting commission, represents the aggregate initial public offering
price net of the applicable sales charge on 10,000 units of fractional
undivided interest of the Trust as of the date of deposit.

Undistributed net investment income includes accumulated accretion of
original issue discount of $ 103,644.


<PAGE>

<TABLE>

 INSURED MUNICIPAL SECURITIES TRUST, 18TH DISCOUNT SERIES

 Portfolio                                    
 December 31, 1993                            


<CAPTION>


Port-    Aggregate                                     Coupon Rate/    Redemption Feature                
folio    Principal       Name of Issuer      Ratings   Date(s) of      S.F.--Sinking Fund          Market
No.        Amount      and Title of Bonds      (1)     Maturity(2)     Ref.--Refunding(2)(7)      Value(3)
- -----    ----------   ---------------------   -----    ------------    --------------------     ------------
<S>      <C>          <C>                     <C>      <C>             <C>                      <C>
 1       $  125,000   Boulder County,          AAA     9.250%          10/01/96 @ 100 S.F.      $   140,309
                      Colorado Hospital                10/01/2010      10/01/95 @ 102 Ref.               
                      Revenue Improvement      
                      and Refunding Bonds      
                      1985 Series (Boulder     
                      Community Hospital       
                      Project) (Financial      
                      Guaranty)(5)             
     
 2          130,000   Palm Beach County,       AAA     10.000          12/01/95 @ 100 S.F.           165,933
                      Florida Solid Waste              12/01/2004      None                              
                      Authority Revenue        
                      Bonds, 1983 Series       
                      (MBIA)                   
     
 3          330,000   City of Atlanta,         AAA     6.300           1/01/00 @ 100 S.F.            333,706
                      Georgia, Airport                 1/01/2007       2/03/94 @ 101 Ref.                
                      Facilities Revenue       
                      Bonds, 1977 Series       
                      (Financial Guaranty)     
     
 4          160,000   City and County of       AAA     8.700           6/01/07 @ 100 S.F.            174,376
                      Honolulu, Hawaii                 12/01/2028      6/01/96 @ 103 Ref.                
                      Multifamily Housing      
                      Revenue Bonds FHA        
                      Insured (Hale Pauchi     
                      Project) 1985 Series     
                      A (MBIA)                 
     
 5          180,000   City of Alton,           AAA     9.250           9/01/00 @ 100 S.F.            199,766
                      Madison County                   9/01/2003       9/01/95 @ 102 Ref.                
                      Illinois Hospital        
                      Facility Revenue         
                      Refunding Bonds, 1985    
                      Series  (Saint           
                      Anthony's Hospital)      
                      (AMBAC)                  
     
 6          250,000   Decatur, Illinois        AAA     9.100           2/01/02 @ 100 S.F.            306,689
                      Sanitation District,             2/01/2005       2/01/99 @ 100 Ref.                
                      General Obligation       
                      Refunding Revenue        
                      Bonds,1985 Series        
                      (Financial Guaranty)     
                      (5)                      
     
 7          100,000   Jasper County Indiana    AAA     10.000          3/01/07 @ 100 S.F.            103,265
                      Hospital Authority               3/01/2009       3/01/94 @ 102 Ref.                
                      Hospital Facility        
                      Revenue Memorial         
                      Hospital and Health      
                      Care Center Project      
                      1984 Series(MBIA) (5)    
     
     
 8          355,000   Davies County,           AAA     9.750           9/01/04 @ 100 S.F.            427,842
                      Kentucky Hospital                9/01/2011       9/01/97 @ 100 Ref.                
                      Revenue Bonds, 1985      
                      Series A  (Mercy         
                      Medical Center)          
                      (AMBAC) (5)              
     
 9          100,000   Kenton County,           AAA     9.000           No Sinking Fund               109,112
                      Kentucky Water                   2/01/2005       2/01/95 @ 103 Ref.                
                      District #1              
                      Waterworks Revenue       
                      Bonds, 1985 Series       
                      (AMBAC) (5)              
     
 10         155,000   Massachusetts Housing    AAA     9.125           12/01/02 @ 100 S.F.           171,326
                      Finance Authority                12/01/2005      12/01/95 @ 103 Ref.               
                      Housing Revenue          
                      Bonds, 1985 Series A     
                      (MBIA)                   
     
 11         250,000   County of Monroe,        AAA     9.625           12/01/96 @ 100 S.F.           284,963
                      Michigan Pollution               12/01/2015      12/01/95 @ 103 Ref.               
                      Control Revenue Bonds    
                      (Detroit Edison          
                      Company Project) 1985    
                      Series A (AMBAC)         
     
 12         120,000   The City of St. Louis    AAA     10.000          7/01/99 @ 100 S.F.            128,152
                      (Missouri) Airport               7/01/2002       7/01/94 @ 103 Ref.                
                      Revenue Bonds, 1984      
                      Series  Lambert-St.      
                      Louis Int'l Airport      
                      (AMBAC) (5)              
     
 13         100,000   Reno, Nevada Hospital    AAA     9.750           7/01/01 @ 100 S.F.            110,985
                      Refunding Revenue                7/01/2004       7/01/95 @ 102 Ref.                
                      Bonds, Saint Mary's      
                      Hospital, 1985 Series    
                      A (MBIA)                 
     
 14         250,000   Cape May County, New     AAA     9.000           1/01/06 @ 100 S.F.            279,425
                      Jersey Municipal                 1/01/2016       1/01/96 @ 102 Ref.                
                      Utilities Authority      
                      Sewer Revenue            
                      Refunding Bonds, 1985    
                      Series (Financial        
                      Guaranty)                
     
 15         515,000   Oklahoma Municipal       AAA     9.250           1/01/06 @ 100 S.F.            582,728
                      Power Authority Power            1/01/2015       1/01/96 @ 102 Ref.                
                      Supply System Revenue    
                      Bonds, 1985 Series C     
                      (MBIA) (5)               
     
 16         250,000   City of Philadelphia,    AAA     9.125           3/15/06 @ 100 S.F.            273,625
                      Pennsylvania Gas                 3/15/2012       3/15/95 @ 102.5 Ref.              
                      Works Revenue Bonds,     
                      1985 Series 9 (AMBAC)    
                      (5)                      
     
 17         495,000   Scranton-Lackawanna      AAA     9.875           3/01/96 @ 100 S.F.            542,525
                      Health and Welfare               3/01/2012       3/01/95 @ 102 Ref.                
                      Authority Hospital       
                      Revenue Refunding        
                      Bonds, 1985 Series       
                      (The Community           
                      Medical Center           
                      Scranton,                
                      Pennsylvania)            
                      (Financial Guaranty)     
                      (5)                      
     
 18         160,000   City of Henderson,       AAA     9.125           No Sinking Fund               212,152
                      Texas (Rusk County)              5/15/2003       None                              
                      General Obligation       
                      Bonds, 1985 Series       
                      (AMBAC)                  
     
 19a        430,000   City of Houston,         AAA     9.375           12/01/06 @ 100 S.F.           487,745
                      Texas Sewer System               12/01/2013      12/01/95 @ 102 Ref.               
                      Junior Lien Revenue      
                      Refunding Bonds, 1985    
                      Series (Financial        
                      Guaranty) (5)            
     
 19b         70,000   City of Houston,         AAA     9.375           12/01/06 @ 100 S.F.            79,400
                      Texas Sewer System               12/01/2013      12/01/95 @ 102 Ref.               
                      Junior Lien Revenue      
                      Refunding Bonds, 1985    
                      Series (Financial        
                      Guaranty) (5)            
     
 20         140,000   Intermountain Power      AAA     9.625           7/01/06 @ 100 S.F.            156,586
                      Agency (a political              7/01/2008       7/01/95 @ 102.5 Ref.              
                      subdivision of the       
                      State of Utah) Power     
                      Supply Revenue           
                      Refunding Bonds, 1985    
                      Series A (AMBAC) (5)     
     
     
 21          90,000   Intermountain Power      AAA     9.125           7/01/13 @ 100 S.F.             99,578
                      Agency (a political              7/01/2018       7/01/95 @ 102 Ref.                
                      subdivision of the       
                      State of Utah) Power     
                      Supply Revenue           
                      Refunding Bonds, 1985    
                      Series D (AMBAC) (5)     
     
 22         255,000   Intermountain Power      AAA     6.500           7/01/13 @ 100 S.F.            267,648
                      Agency (a political              7/01/2014       7/01/95 @ 100 Ref.                
                      subdivision of the       
                      State of Utah) Power     
                      Supply System Revenue    
                      Refunding Bonds, 1985    
                      Series J (MBIA) (5)      
     
 23       3,840,000   The District of          AAA     0.000           5/01/05 @ 11.975 S.F.         154,483
                      Columbia Multi-Unit              11/01/2025      11/01/98 @ 6.415 Ref.             
                      Housing Finance          
                      Corporation Mortgage     
                      Revenue Bonds, 1983      
                      Series  (FHA Insured     
                      Mortgage                 
                      Loan-Congress Park II    
                      Apartments Section 8     
                      Assisted Project)        
                      (MBIA)                   
     
 24       1,060,000   Anne Arundel County,     AAA     0.000           6/01/21 @ 54.504 S.F.          36,135
                      Maryland Economic                6/01/2027       1/06/94 @ 3.409 Ref.              
                      Development Revenue      
                      Bonds, 1985 Series       
                      (FHA Insured Mortgage    
                      Loan-The Regency Club    
                      II Facility) (MBIA)      
                      (5)                      

         ----------                                                                             ------------
      $   9,910,000                                                                          $     5,828,454
         ==========                                                                             ============

  See accompanying footnotes to portfolio and notes to financial statements.
</TABLE>

<PAGE>
     
Footnotes to Portfolio

December 31, 1993


(1) All ratings are by Standard & Poor's Corporation.  A brief description
of the ratings symbols and their meanings is set forth under
"Description of Bond Ratings" in Part B of this Prospectus.

(2) See "The Trust - Portfolio" in Part B of this Prospectus for an
explanation of redemption features.  See "Tax Status" in Part B of
this Prospectus for a statement of the Federal tax consequences to a
Certificateholder upon the sale, redemption or maturity of a bond.

(3) At December 31, 1993, the net unrealized appreciation of all the bonds
was comprised of the following:

    Gross unrealized appreciation         $            138,172
    Gross unrealized depreciation                     (121,018)

    Net unrealized appreciation                     $   17,154

(4) The annual interest income, based upon bonds held at December
31, 1993, (excluding accretion of original issue discount on zero-coupon
bonds) to the Trust is $453,810.

(5)    The bonds have been prerefunded and will be redeemed at the next
refunding call date.

(6) Bonds sold or called after December 31, 1993 are noted in a footnot
"Changes in Trust Portfolio" under "Description of Portfolio" in Part
 of this Prospectus.

(7)  The Bonds may also be subject to other calls, which may be permitted
or required by events which cannot be predicted (such as destruction,
condemnation, termination of a contract, or receipt of excess or
unanticipated revenues).
<PAGE>


                 NOTE:  Part A of This Prospectus May Not Be     
                        Distributed Unless Accompanied by Part B.


                        INSURED MUNICIPAL SECURITIES TRUST

                               19TH DISCOUNT SERIES
                              (MULTIPLIER PORTFOLIO)

                                                                              
       
              The Trust is a unit investment trust designated 19th Discount
    Series ("Insured Municipal Discount Trust") with an underlying portfolio
    of long-term insured tax-exempt bonds issued by or on behalf of states,
    municipalities and public authorities and was formed to preserve capital
    and to provide interest income (including, where applicable, earned
    original issue discount) which, in the opinions of bond counsel to the
    respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law but may be subject to state
    and local taxes.  Capital gains are subject to tax.  (See "Tax Status" and
    "The Trust--Portfolio" in Part B of this Prospectus.)  The Sponsor is
    Bear, Stearns & Co. Inc.  The value of the Units of the Trust will
    fluctuate with the value of the underlying bonds.  Minimum purchase:  1
    Unit. 

                                                                              


              This Prospectus consists of two parts.  Part A contains the
    Summary of Essential Information as of December 31, 1993 (the "Evaluation
    Date"), a summary of certain specific information regarding the Trust and
    audited financial statements of the Trust, including the related
    portfolio, as of the Evaluation Date.  Part B of this Prospectus contains
    a general summary of the Trust.
        
                    Investors should retain both parts of this
                         Prospectus for future reference. 

                                                                              


         THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE
         SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION
         NOR HAS THE COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON
         THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS.  ANY REPRESENTATION TO
         THE CONTRARY IS A CRIMINAL OFFENSE.

       
                      Prospectus Part A Dated April 29, 1994
        



    <PAGE>
       
              THE TRUST.  The Trust is a unit investment trust formed to
    preserve capital and to provide interest income (including, where
    applicable, earned original issue discount) which, in the opinions of bond
    counsel to the respective issuers, is, with certain exceptions, currently
    exempt from regular federal income tax under existing law through
    investment in a fixed, diversified portfolio of long-term insured bonds
    (the "Bonds") issued by or on behalf of states, municipalities and public
    authorities which, because of irrevocable insurance, are rated "AAA" by
    Standard & Poor's Corporation.  Although the Supreme Court has determined
    that Congress has the authority to subject interest on bonds such as the
    Bonds in the Trust to regular federal income taxation, existing law
    excludes such interest from regular federal income tax.  Such interest
    income may, however, be subject to the federal corporate alternative
    minimum tax and to state and local taxes.  (See "Tax Status" in Part B of
    this Prospectus.)  For a list of ratings on the Evaluation Date, see
    "Portfolio."  The Bonds were acquired at prices which resulted in the
    portfolio as a whole being purchased at a deep discount from par value. 
    The portfolio may also include bonds issued at an original issue discount. 
    Additionally, some of the Bonds in the portfolio may be "Zero Coupon
    Bonds," which are original issue discount bonds that provide for payment
    at maturity at par value, but do not provide for the payment of any
    current interest.  Some of the Bonds in the Trust have been issued with
    optional refunding or refinancing provisions ("Refunded Bonds") whereby
    the issuer of the Bond has the right to call such Bond prior to its stated
    maturity date (and other than pursuant to sinking fund provisions) and to
    issue new bonds ("Refunding Bonds") in order to finance the redemption. 
    Issuers typically utilize refunding calls in order to take advantage of
    lower interest rates in the marketplace.  Some of these Refunded Bonds may
    be called for redemption pursuant to pre-refunding provisions ("Pre-
    Refunded Bonds") whereby the proceeds from the issue of the Refunding
    Bonds are typically invested in government securities in escrow for the
    benefit of the holders of the Pre-Refunded Bonds until the refunding call
    date.  Usually, Pre-Refunded Bonds will bear a triple-A rating because of
    this escrow.  The issuers of Pre-Refunded Bonds must call such Bonds on
    their refunding call date.  Therefore, as of such date, the Trust will
    receive the call price for such bonds but will cease receiving interest
    income with respect to them.  For a list of those Bonds which are Pre-
    Refunded Bonds, if any, as of the Evaluation Date, see "Notes to Financial
    Statements" in this Part A.  Some of the Bonds in the portfolio may have
    been purchased at an aggregate premium over par.  All of the Bonds in the
    Trust were rated "AAA" by Standard & Poor's Corporation at the time
    originally deposited in the Trust.  This rating results from insurance
    relating only to the Bonds in the Trust and not to the Units of the Trust. 
    The insurance does not remove market risk, as it does not guarantee the
    market value of the Units.  For a discussion of the significance of such
    ratings, see "Description of Bond Ratings" in Part B of this Prospectus,
    and for a list of ratings on the Evaluation Date see the "Portfolio."  The
    payment of interest and preservation of capital are, of course, dependent
    upon the continuing ability of issuers of the Bonds or the insurers
    thereof to meet their obligations.  There can be no assurance that the
    Trust's investment objectives will be achieved.  Investment in the Trust
    should be made with an understanding of the risks which an investment in
    long-term fixed rate debt obligations may entail, including the risk that
    the value of the underlying portfolio will decline with increases in
    interest rates, and that the value of Zero Coupon Bonds is subject to
    greater fluctuation than coupon bonds in response to changes in interest
    rates.  Each Unit in the Trust represents a 1/15000th undivided interest
    in the principal and net income of the Trust.  The principal amount of
    Bonds deposited in the Trust per Unit is reflected in the Summary of
    Essential Information.  (See "Organization" in Part B of this Prospectus.) 
    The Units being offered hereby are issued and outstanding Units which have
    been purchased by the Sponsor in the secondary market. 

              INSURANCE.  Each of the Bonds in the Trust is insured by a
    municipal bond guaranty insurance policy obtained by either the Sponsor
    ("Sponsor-Insured Bonds") or the issuers of the Bonds ("Pre-Insured
    Bonds") and issued by one of the insurance companies (the "Insurance
    Companies"), described under "Insurance on the Bonds" in Part B of this
    Prospectus, covering scheduled payment of principal thereof and interest
    thereon when such amounts shall become due for payment but shall not have
    been paid by the issuer or any other insurer thereof.  The insurance,
    unless obtained by Municipal Bond Investors Assurance Corporation ("MBIA
    Corp."), will also cover any accelerated payments of principal and the
    increase in interest payments or premiums, if any, payable upon mandatory
    redemption of the Bonds if interest on any Bonds is ultimately deemed to
    be subject to regular federal income tax.  Insurance obtained from MBIA
    Corp. only guarantees the accelerated payments required to be made by or
    on behalf of an issuer of small industrial revenue bonds and pollution
    control bonds if there is an event which results in the loss of tax-exempt
    status of the interest on such Bonds, including principal, interest or
    premium payments, if any, as and when required.  To the extent, therefore,
    that Bonds are only covered by insurance obtained from MBIA Corp., such
    Bonds will not be covered for the accelerated payments required to be made
    by or on behalf of an issuer of other than small industrial revenue bonds
    or pollution control revenue bonds if there occurs an event which results
    in the loss of tax-exempt status of the interest on such Bonds.  None of
    the insurance will cover accelerated payments of principal or penalty
    interest or premiums unrelated to taxability of interest on the Bonds
    (although the insurance, including insurance obtained by MBIA Corp., does
    guarantee payment of principal and interest in such amounts and at such
    times as such amounts would have been due absent such acceleration).  The
    insurance relates only to the prompt payment of principal of and interest
    on the securities in the portfolio, and does not remove market risks or
    guarantee the market value of the Units in the Trust.  The terms of the
    insurance are more fully described under "Insurance on the Bonds" in
    Part B of this Prospectus.  For a discussion of the effect of an
    occurrence of nonpayment of principal or interest on any Bonds in the
    Trust, see "Portfolio Supervision" in Part B of this Prospectus.  No
    representation is made herein as to any Bond insurer's ability to meet its
    obligations under a policy of insurance relating to any of the Bonds.  In
    addition, investors should be aware that, subsequent to the Date of
    Deposit, the rating of the claims-paying ability of the insurer of an
    underlying Bond may be downgraded, which may result in a downgrading of
    the rating of the Units in the Trust.  The approximate percentage of the
    aggregate principal amount of the portfolio that is insured by each
    Insurance Company is as follows:  AMBAC Indemnity Corp. ("AMBAC"), 7.2%;
    Bond Investors Guaranty ("BIG"), 10.9%; Financial Guaranty Insurance
    Company ("Financial Guaranty"), 18.4%; and Municipal Bond Insurance
    Association ("MBIA"), 63.5%. 

              PUBLIC OFFERING PRICE.  The secondary market Public Offering
    Price of each Unit is equal to the aggregate bid price of the Bonds in the
    Trust divided by the number of Units outstanding, plus a sales charge of
    5.5% of the Public Offering Price, or 5.820% of the net amount invested in
    Bonds per Unit.  In addition, accrued interest to the expected date of
    settlement, including earned original issue discount, is added to the
    Public Offering Price.  If Units had been purchased on the Evaluation
    Date, the Public Offering Price per Unit would have been $567.00 plus
    accrued interest of $7.50 under the monthly distribution plan, $10.71
    under the semi-annual distribution plan and $10.76 under the annual
    distribution plan, for a total of $574.50, $577.71 and $577.76,
    respectively.  The Public Offering Price per Unit can vary on a daily
    basis in accordance with fluctuations in the aggregate bid price of the
    Bonds.  (See "Public Offering--Offering Price" in Part B of this
    Prospectus.)

              ESTIMATED LONG TERM RETURN AND ESTIMATED CURRENT RETURN.  The
    rate of return on an investment in Units of the Trust is measured in terms
    of "Estimated Current Return" and "Estimated Long Term Return".

              Estimated Long Term Return is calculated by:  (1) computing the
    yield to maturity or to an earlier call date (whichever results in a lower
    yield) for each Bond in the Trust's portfolio in accordance with accepted
    bond practices, which practices take into account not only the interest
    payable on the Bond but also the amortization of premiums or accretion of
    discounts, if any; (2) calculating the average of the yields for the Bonds
    in the Trust's portfolio by weighing each Bond's yield by the market value
    of the Bond and by the amount of time remaining to the date to which the
    Bond is priced (thus creating an average yield for the portfolio of the
    Trust); and (3) reducing the average yield for the portfolio of the Trust
    in order to reflect estimated fees and expenses of the Trust and the
    maximum sales charge paid by investors.  The resulting Estimated Long Term
    Return represents a measure of the return to investors earned over the
    estimated life of the Trust.  (For the Estimated Long Term Return to
    Certificateholders under the monthly, semi-annual and annual distribution
    plans, see "Summary of Essential Information".)

              Estimated Current Return is a measure of the Trust's cash flow. 
    Estimated Current Return is computed by dividing the Estimated Net Annual
    Interest Income per Unit by the Public Offering Price per Unit.  In
    contrast to the Estimated Long Term Return, the Estimated Current Return
    does not take into account the amortization of premium or accretion of
    discount, if any, on the Bonds in the portfolio of the Trust.  Moreover,
    because interest rates on Bonds purchased at a premium are generally
    higher than current interest rates on newly issued bonds of a similar type
    with comparable rating, the Estimated Current Return per Unit may be
    affected adversely if such Bonds are redeemed prior to their maturity.

              The Estimated Net Annual Interest Income per Unit of the Trust
    will vary with changes in the fees and expenses of the Trustee and the
    Evaluator applicable to the Trust and with the redemption, maturity, sale
    or other disposition of the Bonds in the Trust.  The Public Offering Price
    will vary with changes in the bid prices of the Bonds.  Therefore, there
    is no assurance that the present Estimated Current Return or Estimated
    Long Term Return will be realized in the future.  (For the Estimated
    Current Return to Certificateholders under the monthly, semi-annual and
    annual distribution plans, see "Summary of Essential Information".  See
    "Estimated Long Term Return and Estimated Current Return" in Part B of
    this Prospectus.)

              A schedule of cash flow projections is available from the
    Sponsor upon request.

              DISTRIBUTIONS.  Distributions of interest income, less expenses,
    will be made by the Trust either monthly, semi-annually or annually
    depending upon the plan of distribution applicable to the Unit purchased. 
    A purchaser of a Unit in the secondary market will initially receive
    distributions in accordance with the distribution plan chosen by the prior
    owner of such Unit and may thereafter change the plan as provided under
    "Interest and Principal Distributions" in Part B of this Prospectus. 
    Distributions of principal, if any, will be made semi-annually on June 15
    and December 15 of each year.  (See "Rights of Certificateholders--
    Interest and Principal Distributions" in Part B of this Prospectus.  For
    estimated monthly, semi-annual and annual interest distributions, see
    "Summary of Essential Information.")

              MARKET FOR UNITS.  The Sponsor, although not obligated to do so,
    presently maintains and intends to continue to maintain a secondary market
    for the Units at prices based on the aggregate bid price of the Bonds in
    the Trust portfolio.  The reoffer price will be based on the aggregate bid
    price of the Bonds plus a sales charge of 5.5% of the Public Offering
    Price (5.820% of the net amount invested), plus net accrued interest.  If
    a market is not maintained a Certificateholder will be able to redeem his
    Units with the Trustee at a price also based on the aggregate bid price of
    the Bonds.  (See "Liquidity--Sponsor Repurchase" and "Public Offering--
    Offering Price" in Part B of this Prospectus.)
        
              TOTAL REINVESTMENT PLAN.  Certificateholders under the semi-
    annual and annual plans of distribution have the opportunity to have all
    their regular interest distributions, and principal distributions, if any,
    reinvested in available series of "Insured Municipal Securities Trust" or
    "Municipal Securities Trust."  (See "Total Reinvestment Plan" in Part B of
    this Prospectus.  Residents of Texas see "Total Reinvestment Plan for
    Texas Residents" in Part B of this Prospectus.)  The Plan is not designed
    to be a complete investment program. 


    <PAGE>
       
                        INSURED MUNICIPAL SECURITIES TRUST
                               19TH DISCOUNT SERIES

             SUMMARY OF ESSENTIAL INFORMATION AS OF DECEMBER 31, 1993

    Date of Deposit:  April 24, 1986           Minimum Principal Distribution:
    Principal Amount of Bonds ...$14,400,000    $1.00 per Unit.
    Number of Units .............15,000        Weighted Average Life to
    Fractional Undivided Inter-                Maturity:
      est in Trust per Unit .....1/15000        18.6 Years.
    Principal Amount of                        Minimum Value of Trust:
      Bonds per Unit ............$960.00        Trust may be terminated if
    Secondary Market Public                     value of Trust is less than
      Offering Price**                          $6,000,000 in principal amount
      Aggregate Bid Price                       of Bonds.
        of Bonds in Trust .......$8,037,298+++ Mandatory Termination Date:
      Divided by 15,000 Units ...$535.82        The earlier of December 31,
      Plus Sales Charge of 5.5%                 2035 or the disposition of the
        of Public Offering Price $31.18         last Bond in the Trust.
      Public Offering Price                    Trustee***:  United States Trust 
        per Unit ................$567.00+       Company of New York.
    Redemption and Sponsor's                   Trustee's Annual Fee:  Monthly 
      Repurchase Price                          plan $1.02 per $1,000; semi-
      per Unit ..................$535.82+       annual plan $.54 per $1,000;
                                        +++     and annual plan is $.35 per
                                        ++++    $1,000.
    Excess of Secondary Market                 Evaluator:  Kenny S&P Evaluation
      Public Offering Price                     Services.   
      over Redemption and                      Evaluator's Fee for Each
      Sponsor's Repurchase                      Evaluation:  Minimum of $12
      Price per Unit ............$31.18++++     plus $.25 per each issue of
    Difference between Public                   Bonds in excess of 50 issues
      Offering Price per Unit                   (treating separate maturities
      and Principal Amount per                  as separate issues).
      Unit Premium/(Discount) ...$(393)        Sponsor:  Bear, Stearns & Co.
    Evaluation Time:  4:00 p.m.                Inc.
      New York Time.                           Sponsor's Annual Fee:  Maximum of
                                                $.15 per $1,000 principal
                                                amount of Bonds (see "Trust
                                                Expenses and Charges" in Part B
                                                of this Prospectus).


        PER UNIT INFORMATION BASED UPON INTEREST DISTRIBUTION PLAN ELECTED


                                            Monthly   Semi-Annual   Annual
                                            Option      Option      Option

    Gross annual interest income# .........$43.08       $43.08     $43.08
    Less estimated annual fees and
      expenses ............................  1.62          .99        .78
    Estimated net annual interest          ______       ______     ______
      income (cash)# ......................$41.46       $42.09     $42.30
    Estimated interest distribution# ......  3.45        21.04      42.30
    Estimated daily interest accrual# ..... .1151        .1169      .1175
    Estimated current return#++ ........... 7.31%        7.42%      7.46%
    Estimated long term return++ .......... 3.47%        3.58%      3.62%
    Record dates .......................... 1st of      Dec. 1 and  Dec. 1
                                            each month  June 1
    Interest distribution dates ........... 15th of     Dec. 15 and Dec. 15
                                            each month  June 15
        
    <PAGE>
       *  The Date of Deposit is the date on which the Trust Agreement was
          signed and the deposit of the Bonds with the Trustee made.

      **  For information regarding offering price per Unit and applicable
          sales charge under the Total Reinvestment Plan, see "Total
          Reinvestment Plan" in Part B of this Prospectus. 

     ***  The Trustee maintains its corporate trust office at 770 Broadway,
          New York, New York 10003 (tel. no. 1-800-428-8890).  For information
          regarding redemption by the trustee, see "Trustee Redemption" in
          Part B of this Prospectus.
       
       +  Plus accrued interest to the expected date of settlement
          (approximately five business days after purchase) of $7.50 monthly,
          $10.71 semi-annually and $10.76 annually. 
        
      ++  The estimated current return and estimated long term return are
          increased for transactions entitled to a discount (see "Employee
          Discounts" in Part B of this Prospectus), and are higher under the
          semi-annual and annual options due to lower Trustee's fees and
          expenses.

     +++  Based solely upon the bid side evaluation of the underlying Bonds
          (including, where applicable, undistributed cash from the principal
          account).  Upon tender for redemption, the price to be paid will be
          calculated as described under "Trustee Redemption" in Part B of this
          Prospectus. 

    ++++  See "Comparison of Public Offering Price, Sponsor's Repurchase Price
          and Redemption Price" in Part B of this Prospectus. 

       #  Does not include income accrual from original issue discount bonds,
          if any.


    <PAGE>
       
                          INFORMATION REGARDING THE TRUST
                              AS OF DECEMBER 31, 1993


    DESCRIPTION OF PORTFOLIO*

          The portfolio of the Trust consists of 24 issues representing
    obligations of issuers located in 13 states and the District of Columbia. 
    The Sponsor has participated as a sole underwriter or manager, co-manager
    or member of an underwriting syndicate from which any of the initial
    aggregate principal amount of the Bonds were acquired.  Approximately
    51.0% of the Bonds are obligations of state and local housing authorities;
    approximately 7.1% are hospital revenue bonds; approximately 2.4% were
    issued in connection with the financing of nuclear generating facilities;
    and none are "mortgage subsidy" bonds.  All of the Bonds in the Trust are
    subject to redemption prior to their stated maturity dates pursuant to
    sinking fund or optional call provisions.  The Bonds may also be subject
    to other calls, which may be permitted or required by events which cannot
    be predicted (such as destruction, condemnation, termination of a
    contract, or receipt of excess or unanticipated revenues).  One issue
    representing $500,000 of the principal amount of the Bonds is a general
    obligation bond.  All 23 of the remaining issues representing $13,900,000
    of the principal amount of the Bonds are payable from the income of a
    specific project or authority and are not supported by the issuer's power
    to levy taxes.  The portfolio is divided for purpose of issue as follows: 
    Airport 1, Coal Power 2, Electric and Gas 1, Fair and Exposition 1,
    Federally Insured Mortgage 2, Hospital 4, Hydro-Electric 1, Levee
    Improvement 1, Nuclear Power 1, Pollution Control 3, Sales Tax 1, Sewer
    System 1, Urban Renewal 1, Waste and Sewer 1, and Waterworks and Sewer
    System 2.  For an explanation of the significance of these factors see
    "The Trust--Portfolio" in Part B of this Prospectus. 


    *     Changes in the Trust Portfolio:  From January 1, 1994 to March 24,
          1994, the entire principal amounts of the Bonds in portfolio nos. 2
          and 24 have been called and are no longer contained in the Trust. 
          The entire principal amount of the Bonds in portfolio no. 5 has been
          called pursuant to pre-refunding provisions and is no longer
          contained in the Trust.


          As of December 31, 1993, $7,345,000 (approximately 51.0% of the
    aggregate principal amount of the Bonds) were original issue discount
    bonds.  Of these original issue discount bonds, $7,345,000 (approximately
    51.0% of the aggregate principal amount of the Bonds) were Zero Coupon
    Bonds.  Zero Coupon Bonds do not provide for the payment of any current
    interest and provide for payment at maturity at par value unless sooner
    sold or redeemed.  The market value of Zero Coupon Bonds is subject to
    greater fluctuations than coupon bonds in response to changes in interest
    rates.  Approximately 3.5% of the aggregate principal amount of the Bonds
    in the Trust were purchased at a "market" discount from par value at
    maturity, approximately 45.5% were purchased at a premium and none were
    purchased at par.  For an explanation of the significance of these factors
    see "Discount and Zero Coupon Bonds" in Part B of this Prospectus. 

          None of the Bonds in the Trust are subject to the federal individual
    alternative minimum tax under the Tax Reform Act of 1986.  See "Tax
    Status" in Part B of this Prospectus. 


    <PAGE>
                       FINANCIAL AND STATISTICAL INFORMATION


    Selected data for each Unit outstanding for the periods listed below:
    
    
   
                                                                    Distribu-
                                                                    tions of
                                          Distributions of Interest Principal
                                          During the Period (per Unit)  During
                               Net Asset *           Semi-             the
                    Units Out-   Value    Monthly   Annual  Annual  Period
    Period Ended     standing  Per Unit   Option    Option  Option (Per Unit)

    December 31, 1991 15,000   $604.53    $44.04   $44.70   $44.92   -0- 
    December 31, 1992 15,000    599.07     43.98    44.68    44.92   -0- 
    December 31, 1993 15,000    546.79     42.70    43.40    43.63 $40.46


    *     Net Asset Value per Unit is calculated by dividing net assets as
          disclosed in the "Statement of Net Assets" by the number of Units
          outstanding as of the date of the Statement of Net Assets.  See
          Note 5 of Notes to Financial Statements for a description of the
          components of Net Assets.
        
    <PAGE>
Independent Auditors' Report


The Sponsor, Trustee and Certificateholders
Insured Municipal Securities Trust, 19th Discount Series:


We have audited the accompanying statement of net assets, including the
portfolio, of Insured Municipal Securities Trust, 19th Discount Series as of
December 31, 1993, and the related statements of operations, and changes in
net assets for each of the years in the three year period then ended.  These
financial statements are the responsibility of the Trustee (see note 2).  Our
responsibility is to express an opinion on these financial statements based on
our audits.

We conducted our audits in accordance with generally accepted auditing
standards.  Those standards require that we plan and perform the audit to
obtain reasonable assurance about whether the financial statements are free of
material misstatement.  An audit includes examining, on a test basis, evidence
supporting the amounts and disclosures in the financial statements.  Our
procedures included confirmation of securities owned as of December 31, 1993,
by correspondence with the Trustee.  An audit also includes assessing the
accounting principles used and siGnificant estimates made by management, as
well as evaluating the overall financial statement presentation.  We believe
that our audits provide a reasonable basis for our opinion.

In our opinion, the financial statements referred to above present fairly, in
all material respects, the financial position of Insured Municipal Securities
Trust, 19th Discount Series as of December 31, 1993, and the results of its
operations and the changes in its net assets for each of the years in the
three year period then ended in conformity with generally accepted accounting
principles.




    KPMG Peat Marwick


New York, New York
March 31, 1994
<PAGE>

<TABLE>
                                          Statement of Net Assets

                                 December 31, 1993
<S>                                                                   <C>
       Investments in marketable securities,
          at market value (cost   $8,252,171)                         $  8,037,198

       Excess of other assets over total liabilities                       164,717
                                                                        -----------

       Net assets 15,000 units   of fractional undivided
          interest outstanding,  $546.79 per  unit)                   $  8,201,915
                                                                        -----------
</TABLE>
       See accompanying notes to financial statements.
<PAGE>

<TABLE>
                                    Statements of Operations
<CAPTION>
                                                      Years ended December 31,
                                           -----------  ---- ----------- ---- ---------
                                              1993              1992            1991
                                           -----------       -----------      ---------
<S>                                     <C>                  <C>              <C>
     Investment income - interest       $     692,174           713,871        709,506
                                           -----------       -----------      ---------

     Expenses:
        Trustee's fees                         15,697            15,408         14,696
        Evaluator's fees                        2,670             2,467          2,079
        Sponsor's advisory fee                  2,250             2,250          2,250
                                           -----------       -----------      ---------

                Total expenses                 20,617            20,125         19,025
                                           -----------       -----------      ---------

                Investment income, net        671,557           693,746        690,481
                                           -----------       -----------      ---------

     Realized and unrealized gain (loss)
     on investments:
        Realized gain on bonds
          sold or called                       52,278             -               -
       Unrealized appreciation
          (depreciation) for the year        (256,292)         (111,503)       235,608
                                           -----------       -----------      ---------

                Net increase in net
                  assets resulting
                  from operations       $     467,543           582,243        926,089
                                           ===========       ===========      =========
</TABLE>
     See accompanying notes to financial statements.
<PAGE>
<TABLE>
                           Statements of Changes in Net Assets
<CAPTION>
                                                             Years ended December 31,
                                                    ----------  -  ------------ - ----------
                                                       1993            1992          1991
                                                    ----------     ------------   ----------
<S>                                              <C>               <C>            <C>
     Operations:
        Investment income, net                   $    671,557          693,746      690,481
        Realized gain on bonds
          sold or called                               52,278           -             -
        Unrealized appreciation
          (depreciation) for the year                (256,292)        (111,503)     235,608
                                                    ----------     ------------   ----------

                    Net increase in net
                       assets resulting
                       from operations                467,543          582,243      926,089

     Distributions to Certificateholders:
        Investment income                             644,831          664,039      664,640
        Principal                                     606,900           -             -
                                                    ----------     ------------   ----------

                    Total increase (decrease)        (784,188)         (81,796)     261,449

     Net assets at beginning of year                8,986,103        9,067,899    8,806,450
                                                    ----------     ------------   ----------

     Net assets at end of year (including
        undistributed net investment
        income of   $326,766,   $300,040 and
        $270,333 respectively)                   $  8,201,915        8,986,103    9,067,899
                                                    ----------     ------------   ----------
                                                    ----------     ------------   ----------
</TABLE>
     See accompanying notes to financial statements.
<PAGE>

Notes to Financial Statements

December 31, 1993, 1992 and 1991


(1)    Organization

Insured Municipal Securities Trust, 19th Discount Series (Trust) was
organized on April 24, 1986 by Bear, Stearns & Co. Inc. (Sponsor)
under the laws of the State of New York by a Trust Indenture and
Agreement, and is registered under the Investment Company Act
of 1940.

(2)    Summary of Significant Accounting Policies

United States Trust Company of New York (Trustee) has custody of and
responsibility for the accounting records and financial statements of
the Trust and is responsible for establishing and maintaining a
system of internal control related thereto.

The Trustee is also responsible for all estimates of expenses and
accruals reflected in the Trust's financial statements.  The
accompanying financial statements have been adjusted to record the
unrealized appreciation (depreciation) of investments and to record
interest income and expenses on the accrual basis.

The discount on the zero-coupon bonds is accreted by the interest
method over the respective lives of the bonds.  The accretion of such
discount is included in interest income; however, it is not
distributed until realized in cash upon maturity or sale of the
respective bonds.

Investments are carried at market value which is determined by either
Standard & Poor's Corporation or Moody's Investors Service, Inc.
(Evaluator) as discussed in Footnotes to Portfolio.  The market value
of the investments is based upon the bid prices for the bonds at the
end of the period, except that the market value on the date of
deposit represents the cost to the Trust based on the offering prices
for investments at that date.  The difference between cost (including
accumulated accretion of original issue discount on zero-coupon
bonds) and market value is reflected as unrealized appreciation
(depreciation) of investments.  Securities transactions are recorded
on the trade date.  Realized gains (losses) from securities
transactions are determined on the basis of average cost of the
securities sold or redeemed.

(3)    Income Taxes

The Trust is not subject to Federal income taxes as provided for by
the Internal Revenue Code.

(4)    Trust Administration

The fees and expenses of the Trust are incurred and paid on the basis
set forth under "Trust Expenses and Charges" in Part B of this
Prospectus.

The Trust Indenture and Agreement provides for interest
distributions as often as monthly (depending upon the distribution
plan elected by the Certificateholders).

The Trust Indenture and Agreement further requires that principal
received from the disposition of bonds, other than those bonds sold
in connection with the redemption of units, be distributed to
Certificateholders.

See "Financial and Statistical Information" in Part A of this
Prospectus for the amounts of per unit distributions during the years
ended December 31, 1993, 1992, and 1991.

The Trust Indenture and Agreement also requires the Trust to redeem
units tendered.  No units have been redeemed since the inception of
the Trust.

(5)    Net Assets

At December 31, 1993, the net assets of the Trust represented the
interest of Certificateholders as follows:

Original cost to Certificateholders                     $ 9,147,844
Less initial gross underwriting commission                 (503,100)
                                                          8,644,744


Accumulated cost of bonds sold or called                   (554,722)
Net unrealized depreciation                                (214,973)
Undistributed net investment income                         326,766
Undistributed proceeds from bonds sold or called                100


    Total                                               $ 8,201,915


The original cost to Certificateholders, less the initial gross
underwriting commission, represents the aggregate initial public offering
price net of the applicable sales charge on 15,000 units of fractional
undivided interest of the Trust as of the date of deposit.

Undistributed net investment income includes accumulated accretion of
original issue discount of $162,149.
<PAGE>

<TABLE>
   INSURED MUNICIPAL SECURITIES TRUST, 19TH DISCOUNT SERIES

   Portfolio
   December 31, 1993
<CAPTION>
  Port-    Aggregate                                     Coupon Rate/   Redemption Feature
  folio    Principal        Name of Issuer      Ratings  Date(s) of     S.F.--Sinking Fund          Market
  No.       Amount        and Title of Bonds      (1)    Maturity(2)    Ref.--Refunding (2)(6)     Value(3)
  --     -------------   ---------------------    ----   -----------    ---------------------     ----------
<S>   <C>                <C>                      <C>    <C>            <C>                    <C>
  1   $        110,000   City of Ft. Smith,       AAA    9.750%         2/01/06 @ 100 S.F.     $     120,363
                         Arkansas Water and              2/01/2015      2/01/95 @ 102.5 Ref.
                         Sewer Revenue Bonds,
                         1985 Series (MBIA) (5)

  2            100,000   Georgia Development      AAA    10.375         No Sinking Fund              102,000
                         Authority (Oglethorpe           1/01/2014      1/01/94 @ 102 Ref.
                         Power Corporation
                         Project) Development
                         Authority of Burke
                         County (GA)  Pollution
                         Control Revenue Bonds,
                         1984 Series
                         (Oglethorpe Power
                         Corp. Vogtle Project)
                         (AMBAC)


  3            100,000   Metropolitan Fair and    AAA    8.750          6/01/01 @ 100 S.F.           109,652
                         Exposition Authority            6/01/2005      6/01/95 @ 102 Ref.
                         (Illinois) Dedicated
                         State Tax Revenue
                         Bonds,1985 Series
                         (BIG) (5)


  4            500,000   Chicago (Illinois)       AAA    8.750          6/01/06 @ 100 S.F.           548,260
                         School Finance                  6/01/2009      6/01/95 @ 102 Ref.
                         Authority General
                         Obligation School
                         Assistance Bonds
                         Refunding 1985 Series
                         (Financial Guaranty)
                         (5)


  5            205,000   Village of Evergreen     AAA    10.000         2/01/03 @ 100 S.F.           210,396
                         Park, Cook County,              2/01/2012      2/01/94 @ 102 Ref.
                         Illinois Hospital
                         Facility Revenue
                         Bonds, 1984 Series
                         Little Company of Mary
                         Hospital, Inc. (MBIA)
                         (5)

  6            450,000   The Hospital Authority   AAA    9.125          7/01/01 @ 100 S.F.           497,888
                         of the City of Fort             7/01/2015      7/01/95 @ 102 Ref.
                         Wayne, Indiana
                         Hospital Revenue
                         Refunding Bonds,
                         (Ancilla System
                         Incorporated) 1985
                         Series A (BIG) (5)


  7            400,000   City of Rockport         AAA    9.250          No Sinking Fund              442,320
                         Indiana Fixed Rate              8/01/2014      8/01/95 @ 102 Ref.
                         Pollution Control
                         Revenue Bonds,
                         (Indiana and Michigan
                         Electric Company
                         Project) 1985 Series A
                         (BIG)

  8            300,000   City of Des Moines,      AAA    10.600         6/01/05 @ 100 S.F.           333,717
                         Iowa Urban Renewal Tax          6/01/2014      6/01/95 @ 101 Ref.
                         Increment Revenue
                         Bonds, 1984 Series
                         (Financial Guarnaty)
                         (5)



  9            350,000   Louisiana Energy and     AAA    9.000%         1/01/00 @ 100 S.F.           376,894
                         Power Authority Power           1/01/2004      1/01/95 @ 102 Ref.
                         Project Revenue Bonds
                         (Rodemacher Unit No.
                         2), 1985 Series
                         (Financial Guaranty)
                         (5)


 10            500,000   Jefferson Sales Tax      AAA    8.875          7/01/00 @ 100 S.F.           551,005
                         District (Jefferson             7/01/2005      7/01/95 @ 102 Ref.
                         Parish, Louisiana)
                         Special Sales Tax
                         Revenue Bonds, 1985
                         Series A (Financial
                         Guaranty) (5)

  11           500,000   Board of Levee           AAA    9.300          5/01/03 @ 100 S.F.           549,605
                         Commissioners of the            11/01/2005     5/01/95 @ 102 Ref.
                         Orleans Levee District
                         (Louisiana) Levee
                         Improvement Refunding
                         Bonds, 1985 Series
                         (MBIA) (5)

                              See
 12            500,000   The City of New          AAA    9.000          8/01/06 @ 100 S.F.           559,335
                         Orleans (Louisiana)             8/01/2015      8/01/95 @ 103 Ref.
                         International Airport
                         General Purpose
                         Revenue Bonds, 1985
                         Series  (MBIA)

 13            550,000   County of Monroe,        AAA    9.625          12/01/96 @ 100 S.F.          626,918
                         Michigan Pollution              12/01/2015     12/01/95 @ 103 Ref.
                         Control Revenue Bonds,
                         (Detroit Edison
                         Company Project) 1985
                         Series A (AMBAC)

 14            125,000   City of Williston,       AAA    10.750         6/01/97 @ 100 S.F.           131,846
                         North Dakota Catholic           6/01/2014      6/01/94 @ 102 Ref.
                         Health Corporation
                         Health Facilities
                         Revenue Bonds, (Mercy
                         Hospital, Williston
                         Project) 1984 Series
                         (MBIA) (5)

 15            125,000   Harris County, Texas     AAA    8.600          No Sinking Fund              152,068
                         Municipal Utility               6/01/2002      6/01/99 @ 100 Ref.
                         District #132,
                         Waterworks Sewer
                         System Combined Tax
                         and Revenue Bonds,
                         1985 Series (MBIA)

 16a           430,000   City of Houston, Texas   AAA    9.375          12/01/06 @ 100 S.F.          487,745
                         Sewer System Junior             12/01/2013     12/01/95 @ 102 Ref.
                         Lien Revenue Refunding
                         Bonds, Series 1985
                         (Financial Guaranty)
                         (5)

 16b            70,000   City of Houston, Texas   AAA    9.375          12/01/06 @ 100 S.F.           79,400
                         Sewer System Junior             12/01/2013     12/01/95 @ 102 Ref.
                         Lien Revenue Refunding
                         Bonds, Series 1985
                         (Financial Guaranty)
                         (5)

 17            150,000   Lower Colorado (Texas)   AAA    9.000          1/01/06 @ 100 S.F.           169,006
                         River Authority                 1/01/2009      1/01/96 @ 102 Ref.
                         Priority Refunding
                         Revenue Bonds, 1985
                         Series (BIG) (5)

 18            100,000   City of Pharr, Texas     AAA    9.000          No Sinking Fund              109,384
                         Waterworks and Sewer            9/01/2003      9/01/95 @ 100 Ref.
                         System Construction
                         Refunding and Revenue
                         Bonds, 1985 Series
                         (AMBAC) (5)

 19            475,000   City of San Antonio,     AAA    9.375          2/01/05 @ 100 S.F.           513,271
                         Texas Electric and Gas          2/01/2009      2/01/95 @ 101.5 Ref.
                         System Improvement
                         Bonds, New 1985 Series
                         A (BIG) (5)


 20            275,000   Intermountain Power      AAA    9.625          7/01/06 @ 100 S.F.           307,579
                         Agency (a political             7/01/2008      7/01/95 @ 102.5 Ref.
                         subdivision of the
                         State of Utah) Power
                         Supply Revenue
                         Refunding Bonds, 1985
                         Series A (AMBAC) (5)

 21            500,000   Chelan County            AAA    6.375          6/01/07 @ 100 S.F.           511,285
                         (Washington) Public             6/01/2029      2/03/94 @ 102 Ref.
                         Utility District No. 1
                         Columbia River-Rock
                         Island Hydro-Electric
                         System Refunding
                         Revenue, 1976 Series
                         (Financial Guaranty)

 22a           160,000   Wisconsin Health         AAA    10.625         10/01/02 @ 100 S.F.          171,942
                         Facilities Authority            10/01/2012     10/01/94 @ 102 Ref.
                         Revenue Bonds, 1984
                         Series (Sister of the
                         Sorrowful
                         Mother-Ministry
                         Corporation) (MBIA)
                         (5)

 22b            80,000   Wisconsin Health         AAA    10.625         10/01/02 @ 100 S.F.           85,970
                         Facilities Authority            10/01/2012     10/01/94 @ 102 Ref.
                         Revenue Bonds, 1984
                         Series (Sister of the
                         Sorrowful
                         Mother-Ministry
                         Corporation) (MBIA)

 23          6,345,000   The District of          AAA    0.000          5/01/05 @ 11.975 S.F.        255,259
                         Columbia Multi-Unit             11/01/2025     11/01/98 @ 6.415 Ref.
                         Housing Finance
                         Corporation Mortgage
                         Revenue Bonds, 1983
                         Series  (FHA Insured
                         Mortgage Loan-Congress
                         Park II Apartments
                         Section 8 Assisted
                         Project) (MBIA)

 24          1,000,000   Anne Arundel County,     AAA    0.000          6/01/21 @ 54.504 S.F.         34,090
                         Maryland Economics              6/01/2027      1/06/94 @ 3.409 Ref.
                         Development Revenue
                         Bonds, 1985 Series
                         (FHA Insured Mortgage
                         Loan-The Regency Club
                         II Facility) (MBIA)

         -------------                                                                            ----------
      $     14,400,000                                                                         $   8,037,198
         =============                                                                            ==========
</TABLE>
See accompanying footnotes to portfolio and notes to financial statements.
<PAGE>

Footnotes to Portfolio

December 31, 1993


(1) All ratings are by Standard & Poor's Corporation.  A brief description
of the ratings symbols and their meanings is set forth under
"Description of Bond Ratings" in Part B of this Prospectus.

(2) See "The Trust - Portfolio" in Part B of this Prospectus for an
explanation of redemption features.  See "Tax Status" in Part B of
this Prospectus for a statement of the Federal tax consequences to a
Certificateholder upon the sale, redemption or maturity of a bond.

(3) At December 31, 1993, the net unrealized depreciation of all the bonds
was comprised of the following:

    Gross unrealized appreciation    $                    77,922
    Gross unrealized depreciation                       (292,895)

    Net unrealized depreciation                       $ (214,973)

(4) The annual interest income, based upon bonds held at December 31, 1993,
(excluding accretion of original issue discount on zero-coupon bonds)
to the Trust is $646,213.

(5) The bonds have been prerefunded and will be redeemed at the next
refunding call date.

(6) The Bonds may also be subject to other calls, which may be permitted
or required by events which cannot be predicted (such as destruction,
condemnation, termination of a contract, or receipt of excess or
unanticipated revenues).

<PAGE>

                 NOTE:  Part A of This Prospectus May Not Be     
                        Distributed Unless Accompanied by Part B.


                        INSURED MUNICIPAL SECURITIES TRUST

                                     SERIES 7

                                                                              

       
          The Trust is a unit investment trust designated Series 7 ("Insured
    Municipal Trust") with an underlying portfolio of long-term insured tax-
    exempt bonds issued by or on behalf of states, municipalities and public
    authorities and was formed to preserve capital and to provide interest
    income (including, where applicable, earned original issue discount)
    which, in the opinions of bond counsel to the respective issuers, is, with
    certain exceptions, currently exempt from regular federal income tax under
    existing law but may be subject to state and local taxes.  Capital gains
    are subject to tax.  (See "Tax Status" and "The Trust--Portfolio" in
    Part B of this Prospectus.)  The Sponsor is Bear, Stearns & Co. Inc.  The
    value of the Units of the Trust will fluctuate with the value of the
    underlying bonds.  Minimum purchase:  1 Unit. 

                                                                              


          This Prospectus consists of two parts.  Part A contains the Summary
    of Essential Information as of December 31, 1993 (the "Evaluation Date"),
    a summary of certain specific information regarding the Trust and audited
    financial statements of the Trust, including the related portfolio, as of
    the Evaluation Date.  Part B of this Prospectus contains a general summary
    of the Trust. 

        
                    Investors should retain both parts of this
                         Prospectus for future reference. 

                                                                              


     THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES
     AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE
     COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR
     ADEQUACY OF THIS PROSPECTUS.  ANY REPRESENTATION TO THE CONTRARY IS A
     CRIMINAL OFFENSE.

       
                      Prospectus Part A Dated April 29, 1994
        
    <PAGE>

       
     THE TRUST.  The Trust is a unit investment trust formed to preserve
    capital and to provide interest income (including, where applicable,
    earned original issue discount) which, in the opinions of bond counsel to
    the respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law through investment in a
    fixed, diversified portfolio of long-term insured bonds (the "Bonds")
    issued by or on behalf of states, municipalities and public authorities
    which, because of irrevocable insurance, are rated "AAA" by Standard &
    Poor's Corporation.  Although the Supreme Court has determined that
    Congress has the authority to subject interest on bonds such as the Bonds
    in the Trust to regular federal income taxation, existing law excludes
    such interest from regular federal income tax.  Such interest income may,
    however, be subject to the federal corporate alternative minimum tax and
    to state and local taxes.  (See "Tax Status" in Part B of this
    Prospectus.)  For a list of ratings on the Evaluation Date, see
    "Portfolio."  Some of the Bonds may be "Zero Coupon Bonds", which are
    original issue discount bonds that provide for payment at maturity at par
    value, but do not provide for the payment of any current interest.  Some
    of the Bonds in the Trust have been issued with optional refunding or
    refinancing provisions ("Refunded Bonds") whereby the issuer of the Bond
    has the right to call such Bond prior to its stated maturity date (and
    other than pursuant to sinking fund provisions) and to issue new bonds
    ("Refunding Bonds") in order to finance the redemption.  Issuers typically
    utilize refunding calls in order to take advantage of lower interest rates
    in the marketplace.  Some of these Refunded Bonds may be called for
    redemption pursuant to pre-refunding provisions ("Pre-Refunded Bonds")
    whereby the proceeds from the issue of the Refunding Bonds are typically
    invested in government securities in escrow for the benefit of the holders
    of the Pre-Refunded Bonds until the refunding call date.  Usually, Pre-
    Refunded Bonds will bear a triple-A rating because of this escrow.  The
    issuers of Pre-Refunded Bonds must call such Bonds on their refunding call
    date.  Therefore, as of such date, the Trust will receive the call price
    for such bonds but will cease receiving interest income with respect to
    them.  For a list of those Bonds which are Pre-Refunded Bonds, if any, as
    of the Evaluation Date, see "Notes to Financial Statements" in this
    Part A.  Some of the Bonds in the portfolio may have been purchased at an
    aggregate premium over par.  All of the Bonds in the Trust were rated
    "AAA" by Standard & Poor's Corporation on the Date of Deposit.  This
    rating results from insurance relating only to the Bonds in the Trust and
    not to Units of the Trust.  The insurance does not remove market risk, as
    it does not guarantee the market value of the Units.  For a discussion of
    the significance of such ratings, see "Description of Bond Ratings" in
    Part B of this Prospectus, and for a list of ratings on the Evaluation
    Date see the "Portfolio."  The payment of interest and preservation of
    capital are, of course, dependent upon the continuing ability of issuers
    of the Bonds or the insurers thereof to meet their obligations.  There can
    be no assurance that the Trust's investment objectives will be achieved. 
    Investment in the Trust should be made with an understanding of the risks
    which an investment in long-term fixed rate debt obligations may entail,
    including the risk that the value of the underlying portfolio will decline
    with increases in interest rates, and that the value of Zero Coupon Bonds
    is subject to greater fluctuation than coupon bonds in response to changes
    in interest rates.  Each Unit in the Trust represents a 1/2000th undivided
    interest in the principal and net income of the Trust.  The principal
    amount of Bonds deposited in the Trust per Unit is reflected in the
    Summary of Essential Information.  (See "Organization" in Part B of this
    Prospectus.)  The Units being offered hereby are issued and outstanding
    Units which have been purchased by the Sponsor in the secondary market. 

          INSURANCE.  Each of the Bonds in the Trust is insured by a municipal
    bond guaranty insurance policy obtained by either the Sponsor ("Sponsor-
    Insured Bonds") or the issuers of the Bonds ("Pre-Insured Bonds") and
    issued by one of the insurance companies (the "Insurance Companies"),
    described under "Insurance on the Bonds" in Part B of this Prospectus,
    covering scheduled payment of principal thereof and interest thereon when
    such amounts shall become due for payment but shall not have been paid by
    the issuer or any other insurer thereof.  The insurance, unless obtained
    by Municipal Bond Investors Assurance Corporation ("MBIA Corp."), will
    also cover any accelerated payments of principal and the increase in
    interest payments or premiums, if any, payable upon mandatory redemption
    of the Bonds if interest on any Bonds is ultimately deemed to be subject
    to regular federal income tax.  Insurance obtained from MBIA Corp. only
    guarantees the accelerated payments required to be made by or on behalf of
    an issuer of small industrial revenue bonds and pollution control bonds if
    there is an event which results in the loss of tax-exempt status of the
    interest on such Bonds, including principal, interest or premium payments,
    if any, as and when required.  To the extent, therefore, that Bonds are
    only covered by insurance obtained from MBIA Corp., such Bonds will not be
    covered for the accelerated payments required to be made by or on behalf
    of an issuer of other than small industrial revenue bonds or pollution
    control revenue bonds if there occurs an event which results in the loss
    of tax-exempt status of the interest on such Bonds.  None of the insurance
    will cover accelerated payments of principal or penalty interest or
    premiums unrelated to taxability of interest on the Bonds (although the
    insurance, including insurance obtained by MBIA Corp., does guarantee
    payment of principal and interest in such amounts and at such times as
    such amounts would have been due absent such acceleration).  The insurance
    relates only to the prompt payment of principal of and interest on the
    securities in the portfolio, and does not remove market risks or guarantee
    the market value of the Units in the Trust.  The terms of the insurance
    are more fully described under "Insurance on the Bonds" in Part B of this
    Prospectus.  For a discussion of the effect of an occurrence of nonpayment
    of principal or interest on any Bonds in the Trust, see "Portfolio
    Supervision" in Part B of this Prospectus.  No representation is made
    herein as to any Bond insurer's ability to meet its obligations under a
    policy of insurance relating to any of the Bonds.  In addition, investors
    should be aware that, subsequent to the Date of Deposit, the rating of the
    claims paying ability of the insurer of an underlying Bond may be
    downgraded, which may result in a downgrading of the rating of the Units
    in the Trust.  The approximate percentage of the aggregate principal
    amount of the portfolio that is insured by each insurance company is as
    follows:  AMBAC Indemnity Corp. ("AMBAC"), 26.0%; Bond Investor's Guaranty
    ("BIG"), 10.1%; Financial Guaranty Insurance Company ("Financial
    Guaranty"), 43.8%; and Municipal Bond Insurance Association ("MBIA,
    Inc."), 20.1%. 

          PUBLIC OFFERING PRICE.  The secondary market Public Offering Price
    of each Unit is equal to the aggregate bid price of the Bonds in the Trust
    divided by the number of Units outstanding, plus a sales charge of 4.9% of
    the Public Offering Price, or 5.152% of the net amount invested in Bonds
    per Unit.  In addition, accrued interest to the expected date of
    settlement is added to the Public Offering Price.  If Units had been
    purchased on the Evaluation Date, the Public Offering Price per Unit would
    have been $809.98 plus accrued interest of $12.71 under the monthly
    distribution plan, $17.27 under the semi-annual distribution plan and
    $17.29 under the annual distribution plan, for a total of $822.69, $827.25
    and $827.27, respectively.  The Public Offering Price per Unit can vary on
    a daily basis in accordance with fluctuations in the aggregate bid price
    of the Bonds.  (See "Public Offering--Offering Price" in Part B of this
    Prospectus.)

        

       

          ESTIMATED LONG TERM RETURN AND ESTIMATED CURRENT RETURN.  The rate
    of return on an investment in Units of the Trust is measured in terms of
    "Estimated Current Return" and "Estimated Long Term Return".

          Estimated Long Term Return is calculated by:  (1) computing the
    yield to maturity or to an earlier call date (whichever results in a lower
    yield) for each Bond in the Trust's portfolio in accordance with accepted
    bond practices, which practices take into account not only the interest
    payable on the Bond but also the amortization of premiums or accretion of
    discounts, if any; (2) calculating the average of the yields for the Bonds
    in the Trust's portfolio by weighing each Bond's yield by the market value
    of the Bond and by the amount of time remaining to the date to which the
    Bond is priced (thus creating an average yield for the portfolio of the
    Trust); and (3) reducing the average yield for the portfolio of the Trust
    in order to reflect estimated fees and expenses of the Trust and the
    maximum sales charge paid by investors.  The resulting Estimated Long Term
    Return represents a measure of the return to investors earned over the
    estimated life of the Trust.  (For the Estimated Long Term Return to
    Certificateholders under the monthly, semi-annual and annual distribution
    plans, see "Summary of Essential Information".)

          Estimated Current Return is a measure of the Trust's cash flow. 
    Estimated Current Return is computed by dividing the Estimated Net Annual
    Interest Income per Unit by the Public Offering Price per Unit.  In
    contrast to the Estimated Long Term Return, the Estimated Current Return
    does not take into account the amortization of premium or accretion of
    discount, if any, on the Bonds in the portfolio of the Trust.  Moreover,
    because interest rates on Bonds purchased at a premium are generally
    higher than current interest rates on newly issued bonds of a similar type
    with comparable rating, the Estimated Current Return per Unit may be
    affected adversely if such Bonds are redeemed prior to their maturity.  

        
       
          The Estimated Net Annual Interest Income per Unit of the Trust will
    vary with changes in the fees and expenses of the Trustee and the
    Evaluator applicable to the Trust and with the redemption, maturity, sale
    or other disposition of the Bonds in the Trust.  The Public Offering Price
    will vary with the changes in the bid prices of the Bonds.  Therefore,
    there is no assurance that the present Estimated Current Return or
    Estimated Long Term Return will be realized in the future.  (For the
    Estimated Current Return to Certificateholders under the monthly, semi-
    annual and annual distribution plans, see "Summary of Essential
    Information".  See "Estimated Long Term Return and Estimated Current
    Return" in Part B of this Prospectus.)

          A schedule of cash flow projections is available from the Sponsor
    upon request. 

          DISTRIBUTIONS.  Distributions of interest income, less expenses,
    will be made by the Trust either monthly, semi-annually or annually
    depending upon the plan of distribution applicable to the Unit purchased. 
    A purchaser of a Unit in the secondary market will initially receive
    distributions in accordance with the distribution plan chosen by the prior
    owner of such Unit and may thereafter change the plan as provided under
    "Interest and Principal Distributions" in Part B of the Prospectus. 
    Distributions of principal, if any, will be made semi-annually on June 15
    and December 15 of each year.  (See "Rights of Certificateholders--
    Interest and Principal Distributions" in Part B of this Prospectus.  For
    estimated monthly, semi-annual and annual interest distributions, see
    "Summary of Essential Information.")

        

       
          MARKET FOR UNITS.  The Sponsor, although not obligated to do so,
    presently maintains and intends to continue to maintain a secondary market
    for the Units at prices based on the aggregate bid price of the Bonds in
    the Trust portfolio.  The reoffer price will be based on the aggregate bid
    price of the Bonds plus a sales charge of 4.9% of the Public Offering
    Price (5.152% of the net amount invested), plus net accrued interest.  If
    a market is not maintained a Certificateholder will be able to redeem his
    Units with the Trustee at a price also based on the aggregate bid price of
    the Bonds.  (See "Liquidity--Sponsor Repurchase" and "Public Offering--
    Offering Price" in Part B of this Prospectus.)

        

          TOTAL REINVESTMENT PLAN.  Certificateholders under the semi-annual
    and annual plans of distribution have the opportunity to have all their
    regular interest distributions, and principal distributions, if any,
    reinvested in available series of "Insured Municipal Securities Trust" or
    "Municipal Securities Trust."  (See "Total Reinvestment Plan" in Part B of
    this Prospectus.  Residents of Texas, see "Total Reinvestment Plan for
    Texas Residents" in Part B of this Prospectus.)  The Plan is not designed
    to be a complete investment program. 


    <PAGE>
       
                        INSURED MUNICIPAL SECURITIES TRUST 

                                     SERIES 7

             SUMMARY OF ESSENTIAL INFORMATION AS OF DECEMBER 31, 1993

    Date of Deposit:  April 24, 1986           Minimum Principal Distribution:
    Principal Amount of Bonds ...$1,540,000     $1.00 per Unit.
    Number of Units .............2,000         Weighted Average Life to
    Fractional Undivided Inter-                Maturity:
      est in Trust per Unit .....1/2000         11.0 Years.
    Principal Amount of                        Minimum Value of Trust:
      Bonds per Unit ............$770.00        Trust may be terminated if
    Secondary Market Public                     value of Trust is less than
      Offering Price**                          $800,000 in principal amount of
      Aggregate Bid Price                       Bonds.
        of Bonds in Trust .......$1,540,582+++ Mandatory Termination Date:
      Divided by 2,000 Units ....$770.29        The earlier of December 31,
      Plus Sales Charge of 4.9%                 2035 or the disposition of the
        of Public Offering Price $39.69         last Bond in the Trust.
      Public Offering Price                    Trustee***:  United States Trust 
        per Unit ................$809.98+       Company of New York.
    Redemption and Sponsor's                   Trustee's Annual Fee:  Monthly 
      Repurchase Price                          plan $1.02 per $1,000; semi-
      per Unit ..................$770.29+       annual plan $.54 per $1,000;
                                        +++     and annual plan is $.35 per
                                        ++++    $1,000.
    Excess of Secondary Market                 Evaluator:  Kenny S&P Evaluation
      Public Offering Price                     Services. 
      over Redemption and                      Evaluator's Fee for Each
      Sponsor's Repurchase                      Evaluation:  Minimum of $12
      Price per Unit ............$39.69++++     plus $.25 per each issue of
    Difference between Public                   Bonds in excess of 50 issues
      Offering Price per Unit                   (treating separate maturities
      and Principal Amount per                  as separate issues).
      Unit Premium/(Discount) ...$39.98        Sponsor:  Bear, Stearns & Co.
    Evaluation Time:  4:00 p.m.                Inc.
      New York Time.                           Sponsor's Annual Fee:  Maximum of
                                                $.15 per $1,000 principal
                                                amount of Bonds (see "Trust
                                                Expenses and Charges" in Part B
                                                of this Prospectus).


        PER UNIT INFORMATION BASED UPON INTEREST DISTRIBUTION PLAN ELECTED

                                            Monthly   Semi-Annual   Annual
                                            Option      Option      Option


    Gross annual interest income# .........$60.53       $60.53     $60.53
    Less estimated annual fees and
      expenses ............................  2.07         1.54       1.38
    Estimated net annual interest          ______       ______     ______
      income (cash)# ......................$58.46       $58.99     $59.15
    Estimated interest distribution# ......  4.87        29.49      59.15
    Estimated daily interest accrual# ..... .1623        .1638      .1643
    Estimated current return#++ ........... 7.22%        7.28%      7.30%
    Estimated long term return++ .......... 2.82%        2.89%      2.91%
    Record dates .......................... 1st of    Dec. 1 and    Dec. 1
                                          each month  June 1
    Interest distribution dates ........... 15th of   Dec. 15 and   Dec. 15
                                          each month  June 15
        
    <PAGE>
       *  The Date of Deposit is the date on which the Trust Agreement was
          signed and the deposit of the Bonds with the Trustee made. 

      **  For information regarding offering price per Unit and applicable
          sales charge under the Total Reinvestment Plan, see "Total
          Reinvestment Plan" in Part B of this Prospectus. 

     ***  The Trustee maintains its corporate trust office at 770 Broadway,
          New York, New York 10003 (tel. no.:  1-800-428-8890).  For
          information regarding redemption by the Trustee, see "Trustee
          Redemption" in Part B of this Prospectus.

       
       +  Plus accrued interest to the expected date of settlement
          (approximately five business days after purchase) of $12.71 monthly,
          $17.27 semi-annually and $17.29 annually. 

        
      ++  The estimated current return and estimated long term return are
          increased for transactions entitled to a discount (see "Employee
          Discounts" in Part B of this Prospectus), and are higher under the
          semi-annual and annual options due to lower Trustee's fees and
          expenses.

     +++  Based solely upon the bid side evaluation of the underlying Bonds
          (including, where applicable, undistributed cash from the principal
          account).  Upon tender for redemption, the price to be paid will be
          calculated as described under "Trustee Redemption" in Part B of this
          Prospectus. 

    ++++  See "Comparison of Public Offering Price, Sponsor's Repurchase Price
          and Redemption Price" in Part B of this Prospectus. 

       #  Does not include income accrual from original issue discount bonds,
          if any.


    <PAGE>
       
                          INFORMATION REGARDING THE TRUST
                              AS OF DECEMBER 31, 1993


    DESCRIPTION OF PORTFOLIO*

          The portfolio of the Trust consists of 12 issues representing
    obligations of issuers located in 10 states.  The Sponsor has not
    participated as a sole underwriter or manager, co-manager or member of an
    underwriting syndicate from which any of the initial aggregate principal
    amount of the Bonds were acquired.  Approximately 7.8% of the Bonds are
    obligations of state and local housing authorities; approximately 20.1%
    are hospital revenue bonds; none were issued in connection with the
    financing of nuclear generating facilities; and none are "mortgage
    subsidy" bonds.  All of the Bonds in the Trust are subject to redemption
    prior to their stated maturity dates pursuant to sinking fund or optional
    call provisions.  The Bonds may also be subject to other calls, which may
    be permitted or required by events which cannot be predicted (such as
    destruction, condemnation, termination of a contract, or receipt of excess
    or unanticipated revenues).  One issue representing $200,000 of the
    principal amount of the Bonds is a general obligation bond.  All 11 of the
    remaining issues representing $1,340,000 of the principal amount of the
    Bonds are payable from the income of a specific project or authority and
    are not supported by the issuer's power to levy taxes.  The portfolio is
    divided for purpose of issue as follows:  Coal Power 1, Federally Insured
    Mortgage 1, Hospital 3, Hydro-Electric 1, Pollution Control 2, Sales Tax
    1, Solid Waste 1 and Urban Renewal 1.  For an explanation of the
    significance of these factors see "The Trust--Portfolio" in Part B of this
    Prospectus.

    *     Changes in the Trust Portfolio:  From January 1, 1994 to March 24,
    1994, the entire principal amount of the Bonds in portfolio no. 2 has been
    called pursuant to pre-refunding provisions and is no longer contained in
    the Trust.  The entire principal amount of the Bonds in portfolio no. 12
    has been called and is no longer contained in the Trust.  50 Units have
    been redeemed from the Trust.
        
    <PAGE>

          As of December 31, 1993, $120,000 (approximately 7.8% of the
    aggregate principal amount of the Bonds) were original issue discount
    bonds.  Of these original issue discount bonds, $120,000 (approximately
    7.8% of the aggregate principal amount of the Bonds) were Zero Coupon
    Bonds.  Zero Coupon Bonds do not provide for the payment of any current
    interest and provide for payment at maturity at par value unless sooner
    sold or redeemed.  The market value of Zero Coupon Bonds is subject to
    greater fluctuations than coupon bonds in response to changes in interest
    rates.  Approximately 28.2% of the aggregate principal amount of the Bonds
    in the Trust were purchased at a "market" discount from par value at
    maturity, approximately 64.0% were purchased at a premium and none were
    purchased at par.  For an explanation of the significance of these factors
    see "Discount and Zero Coupon Bonds" in Part B of this Prospectus.  All of
    the Bonds are subject to redemption prior to maturity pursuant to sinking
    fund or call provisions. 

          None of the Bonds in the Trust are subject to the federal individual
    alternative minimum tax under the Tax Reform Act of 1986.  See "Tax
    Status" in Part B of this Prospectus. 

    <PAGE>
                       FINANCIAL AND STATISTICAL INFORMATION


    Selected data for each Unit outstanding for the periods listed below:
       
                                                                    Distribu-
                                                                    tions of
                                          Distributions of Interest Principal
                                          During the Period (per Unit)  During
                               Net Asset *           Semi-             the
                    Units Out-   Value    Monthly   Annual  Annual  Period
    Period Ended     standing  Per Unit   Option    Option  Option (Per Unit)
 
    December 31, 1991  2,000 $1,037.54    $77.04   $77.96   $77.97    -0-
    December 31, 1992  2,000    938.51     70.52    71.21    71.40$ 94.35
    December 31, 1993  2,000    784.10     63.58    64.20    64.37 139.62

    *     Net Asset Value per Unit is calculated by dividing net assets as
          disclosed in the "Statement of Net Assets" by the number of Units
          outstanding as of the date of the Statement of Net Assets.  See
          Note 5 of Notes to Financial Statements for a description of the
          components of Net Assets.
        
<PAGE>


Independent Auditors' Report


The Sponsor, Trustee and Certificateholders
Insured Municipal Securities Trust, Series 7:


We have audited the accompanying statement of net assets, including the
portfolio, of Insured Municipal Securities Trust, Series 7 as of December
31, 1993, and the related statements of operations, and changes in net
assets for each of the years in the three year period then ended.
These financial statements are the responsibility of the Trustee
(see note 2).  Our responsibility is to express an opinion on these
financial statements based on our audits.

We conducted our audits in accordance with generally accepted auditing
standards.  Those standards require that we plan and perform the audit to
obtain reasonable assurance about whether the financial statements are
free of material misstatement.  An audit includes examining, on a test
basis, evidence supporting the amounts and disclosures in the financial
statements.  Our procedures included confirmation of securities owned
as of December 31, 1993, by correspondence with the Trustee.  An audit
also includes assessing the accounting principles used and significant
estimates made by management, as well as evaluating the overall financial
statement presentation.  We believe that our audits provide a reasonable
basis for our opinion.

In our opinion, the financial statements referred to above present fairly,
in all material respects, the financial position of Insured Municipal
Securities Trust, Series 7 as of December 31, 1993, and the results of
its operations and the changes in its net assets for each of the years
in the three year period then ended in conformity with generally accepted
accounting principles.




    KPMG Peat Marwick


New York, New York
March 31, 1994

<PAGE>

                              Statement of Net Assets

                                 December 31, 1993
                       
       Investments in marketable securities,     
          at market value (cost $1,532,262)                $   1,540,572
                       
       Excess of other assets over total liabilities              27,621
                                                              -----------
                       
       Net assets 2,000 units   of fractional undivided                     
          interest outstanding, $784.10 per  unit)         $   1,568,193
                                                              ===========

       See accompanying notes to financial statements.
<PAGE>

<TABLE>
                              Statements of Operations
<CAPTION>
                                                            Years ended December 31,     
                                                  ----------- ---  ----------- ---- -----------
                                                     1993             1992             1991
                                                  -----------      -----------      -----------
<S>                                            <C>                 <C>              <C>
     Investment income - interest              $     130,392          144,986          159,179
                                                  -----------      -----------      -----------
  
     Expenses:                      
        Trustee's fees                                 2,879            3,000            2,906
        Evaluator's fees                                 889              822              693
        Sponsor's advisory fee                           272              300              300
                                                  -----------      -----------      -----------
  
                Total expenses                         4,040            4,122            3,899
                                                  -----------      -----------      -----------
  
                Investment income, net               126,352          140,864          155,280
                                                  -----------      -----------      -----------
  
     Realized and unrealized gain   
       (loss) on investments:       
          Net realized gain (loss) on
             bonds sold or called                     16,453          (21,321)           -
          Unrealized appreciation   
            (depreciation) for the year              (44,629)          12,830           63,012
                                                  -----------      -----------      -----------
  
                Net gain (loss)     
                  on investments                     (28,176)          (8,491)          63,012
                                                  -----------      -----------      -----------
  
                Net increase in net 
                  assets resulting  
                  from operations              $      98,176          132,373          218,292
                                                  ===========      ===========      ===========

     See accompanying notes to financial statements.
</TABLE>

<PAGE>

<TABLE>

                       Statements of Changes in Net Assets
<CAPTION>
                                                      Years ended December 31,
                                            ----------- --- ------------ --- ------------
                                               1993             1992             1991
                                            -----------     ------------     ------------
<S>                                       <C>               <C>              <C>
Operations:                   
   Investment income, net                 $    126,352          140,864          155,280
   Net realized gain (loss) on
     bonds sold or called                       16,453          (21,321)          -
   Unrealized appreciation    
     (depreciation) for the year               (44,629)          12,830           63,012
                                            -----------     ------------     ------------

           Net increase in net
              assets resulting
              from operations                   98,176          132,373          218,292
                                            -----------     ------------     ------------

Distributions to Certificateholders:
   Investment income                           127,766          141,730          154,805
   Principal                                   279,240          188,700           -
                                            -----------     ------------     ------------

           Total distributions                 407,006          330,430          154,805
                                            -----------     ------------     ------------

           Total increase (decrease)          (308,830)        (198,057)          63,487

Net assets at beginning of year              1,877,023        2,075,080        2,011,593
                                            -----------     ------------     ------------

Net assets at end of year (including
   undistributed net investment
   income o$29,984,  $31,398 and
   $32,264 respectively)                  $  1,568,193        1,877,023        2,075,080
                                            ===========     ============     ============

See accompanying notes to financial statements.
</TABLE>

<PAGE>


INSURED MUNICIPAL SECURITIES TRUST, SERIES 7

Notes to Financial Statements

December 31, 1993, 1992 and 1991


(1)    Organization

Insured Municipal Securities Trust, Series 7 (Trust) was organized on
April 24, 1986 by Bear, Stearns & Co. Inc. (Sponsor) under the laws
of the State of New York by a Trust Indenture and Agreement, and is
registered under the Investment Company Act of 1940.

(2)    Summary of Significant Accounting Policies

United States Trust Company of New York (Trustee) has custody of and
responsibility for the accounting records and financial statements of
the Trust and is responsible for establishing and maintaining a
system of internal control related thereto.

The Trustee is also responsible for all estimates of expenses and
accruals reflected in the Trust's financial statements.  The
accompanying financial statements have been adjusted to record the
unrealized appreciation (depreciation) of investments and to record
interest income and expenses on the accrual basis.

The discount on the zero-coupon bonds is accreted by the interest
method over the respective lives of the bonds.  The accretion of such
discount is included in interest income; however, it is not
distributed until realized in cash upon maturity or sale of the
respective bonds.

Investments are carried at market value which is determined by either
Standard & Poor's Corporation or Moody's Investors Service, Inc.
(Evaluator) as discussed in Footnotes to Portfolio.  The market value
of the investments is based upon the bid prices for the bonds at the
end of the period, except that the market value on the date of
deposit represents the cost to the Trust based on the offering prices
for investments at that date.  The difference between cost (including
accumulated accretion of original issue discount on zero-coupon
bonds) and market value is reflected as unrealized appreciation
(depreciation) of investments.  Securities transactions are recorded
on the trade date.  Realized gains (losses) from securities
transactions are determined on the basis of average cost of the
securities sold or redeemed.

(3)    Income Taxes

The Trust is not subject to Federal income taxes as provided for by
the Internal Revenue Code.

(4)    Trust Administration

The fees and expenses of the Trust are incurred and paid on the basis
set forth under "Trust Expenses and Charges" in Part B of this
Prospectus.

The Trust Indenture and Agreement provides for interest distributions
as often as monthly (depending upon the distribution plan elected by
the Certificateholders).

The Trust Indenture and Agreement further requires that principal
received from the disposition of bonds, other than those bonds sold
in connection with the redemption of units, be distributed to
Certificateholders.

See "Financial and Statistical Information" in Part A of this
Prospectus for the amounts of per unit distributions during the years
ended December 31, 1993, 1992, and 1991.

The Trust Indenture and Agreement also requires the Trust to redeem
units tendered.  No units have been redeemed since the inception of
the Trust.

(5)    Net Assets

At December 31, 1993, the net assets of the Trust represented the
interest  of Certificateholders as follows:

    Original cost to Certificateholders               $ 2,105,887
    Less initial gross underwriting commission           (103,180)
                                                        2,002,707

    Cost of securities sold or called                    (472,818)
    Net unrealized appreciation                             8,310
    Undistributed net investment income                     29,984
    Undistributed proceeds from bonds
    called or sold                                              10
      
              Total                                     $ 1,568,193


    The original cost to Certificateholders, less the initial gross
underwriting commission, represents the aggregate initial public offering
price net of the applicable sales charge on 2,000 units of fractional
undivided interest of the Trust as of the date of deposit.

Undistributed net investment income includes accumulated accretion of
original issue discount of $2,373.

<PAGE>

<TABLE>

INSURED MUNICIPAL SECURITIES TRUST,  SERIES 7
  
Portfolio
 December 31, 1993                     

<CAPTION>

Port-   Aggregate                                   Coupon Rate/   Redemption Feature     
foliO   Principal       Name of Issuer     Ratings  Date(s) of     S.F.--Sinking Fund          Market
No.     Amount       and Title of Bonds     (1)    Maturity(2)    Ref.--Refunding (2) (7)    Value(3)
- --     ---------    ---------------------   ----   ------------   ----------------------     ---------
<S>   <C>           <C>                     <C>    <C>            <C>                     <C>
1     $  200,000    Chicago (Illinois)      AAA    8.750%         6/01/06 @ 100 S.F.      $    219,304
                    School Finance                 6/01/2009      6/01/95 @ 102 Ref.             
                    Authority General       
                    Obligation School       
                    Assistance Bonds        
                    Refunding 1985 Series   
                    (Financial Guaranty)    
                    (5)                     
          
          
2         55,000    Village of Evergreen    AAA    9.875          2/01/00 @ 100 S.F.            56,442
                    Park, Cook County,             2/01/2002      2/01/94 @ 102 Ref.             
                    Illinois Hospital       
                    Facility Revenue        
                    Refunding Bonds, 1984   
                    Series Little Company   
                    of Mary Hospital,       
                    Inc. (MBIA) (5)         
          
          
3        155,000    The Hospital            AAA    9.500          7/01/01 @ 100 S.F.           172,341
                    Authority of the City          7/01/2018      7/01/95 @ 102 Ref.             
                    of     Ft. Wayne,       
                    Indiana Hospital        
                    Revenue (Ancilla        
                    System Inc.) 1985       
                    Series B (BIG) (5)      
          
          
4        100,000    Hospital Authority of   AAA    6.500          No Sinking Fund              103,662
                    St. Joseph County              7/01/2007      7/01/94 @ 102 Ref.             
                    Indiana 1st Mortgage    
                    Hospital Facilities     
                    Refunding Revenue       
                    Bonds 1978 (South       
                    Bend Osteopathic        
                    Hospital Project)       
                    (AMBAC)                 
          
5         75,000    City of Des Moines,     AAA    10.600         6/01/05 @ 100 S.F.            83,429
                    Iowa Urban Renewal             6/01/2014      6/01/95 @ 101 Ref.             
                    Tax Increment Revenue   
                    Bonds, 1984 Series      
                    (Financial Guaranty)    
                    (5)                     
          
6        200,000    Jefferson Sales Tax     AAA    8.875          7/01/00 @ 100 S.F.           220,402
                    District (Jefferson            7/01/2005      7/01/95 @ 102 Ref.             
                    Parish, Louisiana)      
                    Special Sales Tax       
                    Revenue Bonds 1985      
                    Series A (Financial     
                    Guaranty) (5)           
          
7        200,000    County of Monroe,       AAA    9.625          12/01/96 @ 100 S.F.          227,970
                    Michigan Pollution             12/01/2015     12/01/95 @ 103 Ref.            
                    Control Revenue Bonds   
                    (Detroit Edison         
                    Company Project) 1985   
                    Series A (AMBAC)        
          
 8  $     50,000    Mercer County, North    AAA    10.500%        6/30/09 @ 100 S.F.      $     54,575
                    Dakota Pollution               6/30/2013      12/30/94 @ 102 Ref.            
                    Control Revenue         
                    Bonds, 1984 Series      
                    (Basin Electric Power   
                    Cooperative -           
                    Antelope Valley         
                    Station) (AMBAC)        
          
                         See                
9         50,000    Tulsa Public            AAA    10.375         5/01/05 @ 100 S.F.            52,146
                    Facilities Oklahoma            5/01/2007      5/01/94 @ 102 Ref.             
                    Solid Waste, Steam      
                    and Electric (Odgen     
                    Martin Systems) 1984    
                    Series  (AMBAC)         
          
          
10       135,000    Intermountain Power     AAA    6.500          7/01/13 @ 100 S.F.           141,696
                    Agency (a political            7/01/2014      7/01/95 @ 100 Ref.             
                    subdivision of the      
                    State of Utah) Power    
                    Supply System Revenue   
                    Refunding Bonds 1985    
                    Series J (MBIA) (5)     
          
          
11       200,000    Chelan County           AAA    6.375          6/01/07 @ 100 S.F.           204,514
                    Washington Public              6/01/2029      2/3/94 @ 102 Ref.              
                    Utility District No.    
                    1 Columbia River-Rock   
                    Island Hydro-Electric   
                    System Refunding        
                    Revenue, Issue of       
                    1976 Series             
                    (Financial Guaranty)    
          
12       120,000    Anne Arundel County,    AAA    0.000          6/01/21  @ 54.504 S.F.         4,091
                    Maryland Economic              6/01/2027      1/06/94 @ 3.409 Ref.           
                    Development Revenue     
                    Bonds, 1985 Series      
                    (FHA Insured Mortgage   
                    Loan - The Regency      
                    Club II Facility)       
                    (MBIA) (5)              
       ---------                                                                             ---------
    $  1,540,000                                                                          $  1,540,572
       =========                                                                             =========

See accompanying footnotes to portfolio and notes to financial statements.

</TABLE>

<PAGE>

INSURED MUNICIPAL SECURITIES TRUST, SERIES 7

Footnotes to Portfolio

December 31, 1993

(1) All ratings are by Standard & Poor's Corporation.  A brief
description of the ratings symbols and their meanings is set forth
under "Description of Bond Ratings" in Part B of this Prospectus.

(2)  See "The Trust - Portfolio" in Part B of this Prospectus for an
explanation of redemption features.  See "Tax Status" in Part B of
this Prospectus for a statement of the Federal tax consequences to a
Certificateholder upon the sale, redemption or maturity of a bond.

(3) At December 31, 1993, the net unrealized appreciation of all the bonds
was comprised of the following:

    Gross unrealized appreciation                   $  54,373
    Gross unrealized depreciation                     (46,063)

    Net unrealized appreciation                     $   8,310

(4)    The annual interest income, based upon bonds held at December
31, 1993, (excluding accretion of original issue discount on zero-coupon
bonds) to the Trust is $121,069.

(5)  The bonds have been prerefunded and will be redeemed at the next
refunding call date.

(6)  Bonds sold or called after December 31, 1993 are noted in a footnote
"Changes in Trust Portfolio" under "Description of Portfolio" in Part
A of this Prospectus.

(7) The Bonds may also be subject to other calls, which may be permitted
or required by events which cannot be predicted (such as destruction,
condemnation, termination of a contract, or receipt of excess or
unanticipated revenues).
<PAGE>

                 NOTE:  Part A of This Prospectus May Not Be     
                        Distributed Unless Accompanied by Part B.


                        INSURED MUNICIPAL SECURITIES TRUST

                               20TH DISCOUNT SERIES
                              (MULTIPLIER PORTFOLIO)


                                                                              
       
          The Trust is a unit investment trust designated 20th Discount Series
    ("Insured Municipal Discount Trust") with an underlying portfolio of long-
    term insured tax-exempt bonds issued by or on behalf of states,
    municipalities and public authorities and was formed to preserve capital
    and to provide interest income (including, where applicable, earned
    original issue discount) which, in the opinions of bond counsel to the
    respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law but may be subject to state
    and local taxes.  Capital gains are subject to tax.  (See "Tax Status" and
    "The Trust--Portfolio" in Part B of this Prospectus.)  The Sponsor is
    Bear, Stearns & Co. Inc.  The value of the Units of the Trust will
    fluctuate with the value of the underlying bonds.  Minimum purchase:  1
    Unit. 

                                                                              


          This Prospectus consists of two parts.  Part A contains the Summary
    of Essential Information as of December 31, 1993 (the "Evaluation Date"),
    a summary of certain specific information regarding the Trust and audited
    financial statements of the Trust, including the related portfolio, as of
    the Evaluation Date.  Part B of this Prospectus contains a general summary
    of the Trust. 
        
                    Investors should retain both parts of this
                         Prospectus for future reference. 

                                                                              


     THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES
     AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE
     COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR
     ADEQUACY OF THIS PROSPECTUS.  ANY REPRESENTATION TO THE CONTRARY IS A
     CRIMINAL OFFENSE.

       
                      Prospectus Part A Dated April 29, 1994
        
    <PAGE>
       
          THE TRUST.  The Trust is a unit investment trust formed to preserve
    capital and to provide interest income (including, where applicable,
    earned original issue discount) which, in the opinions of bond counsel to
    the respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law through investment in a
    fixed, diversified portfolio of long-term insured bonds (the "Bonds")
    issued by or on behalf of states, municipalities and public authorities
    which, because of irrevocable insurance, are rated "AAA" by Standard &
    Poor's Corporation.  Although the Supreme Court has determined that
    Congress has the authority to subject interest on bonds such as the Bonds
    in the Trust to regular federal income taxation, existing law excludes
    such interest from regular federal income tax.  Such interest income may,
    however, be subject to the federal corporate alternative minimum tax and
    to state and local taxes.  (See "Tax Status" in Part B of this
    Prospectus.)  For a list of ratings on the Evaluation Date, see
    "Portfolio."  The Bonds were acquired at prices which resulted in the
    portfolio as a whole being purchased at a deep discount from par value. 
    The portfolio may also include bonds issued at an original issue discount. 
    Additionally, some of the Bonds in the portfolio may be "Zero Coupon
    Bonds," which are original issue discount bonds that provide for payment
    at maturity at par value, but do not provide for the payment of any
    current interest.  Some of the Bonds in the Trust have been issued with
    optional refunding or refinancing provisions ("Refunded Bonds") whereby
    the issuer of the Bond has the right to call such Bond prior to its stated
    maturity date (and other than pursuant to sinking fund provisions) and to
    issue new bonds ("Refunding Bonds") in order to finance the redemption. 
    Issuers typically utilize refunding calls in order to take advantage of
    lower interest rates in the marketplace.  Some of these Refunded Bonds may
    be called for redemption pursuant to pre-refunding provisions ("Pre-
    Refunded Bonds") whereby the proceeds from the issue of the Refunding
    Bonds are typically invested in government securities in escrow for the
    benefit of the holders of the Pre-Refunded Bonds until the refunding call
    date.  Usually, Pre-Refunded Bonds will bear a triple-A rating because of
    this escrow.  The issuers of Pre-Refunded Bonds must call such Bonds on
    their refunding call date.  Therefore, as of such date, the Trust will
    receive the call price for such bonds but will cease receiving interest
    income with respect to them.  For a list of those Bonds which are Pre-
    Refunded Bonds, if any, as of the Evaluation Date, see "Notes to Financial
    Statements" in this Part A.  Some of the Bonds in the portfolio may have
    been purchased at an aggregate premium over par.  All of the Bonds in the
    Trust were rated "AAA" by Standard & Poor's Corporation at the time
    originally deposited in the Trust.  This rating results from insurance
    relating only to the Bonds in the Trust and not to the Units of the Trust. 
    The insurance does not remove market risk, as it does not guarantee the
    market value of the Units.  For a discussion of the significance of such
    ratings, see "Description of Bond Ratings" in Part B of this Prospectus,
    and for a list of ratings on the Evaluation Date see the "Portfolio."  The
    payment of interest and preservation of capital are, of course, dependent
    upon the continuing ability of issuers of the Bonds or the insurers
    thereof to meet their obligations.  There can be no assurance that the
    Trust's investment objectives will be achieved.  Investment in the Trust
    should be made with an understanding of the risks which an investment in
    long-term fixed rate debt obligations may entail, including the risk that
    the value of the underlying portfolio will decline with increases in
    interest rates, and that the value of Zero Coupon Bonds is subject to
    greater fluctuation than coupon bonds in response to changes in interest
    rates.  Each Unit in the Trust represents a 1/12447th undivided interest
    in the principal and net income of the Trust.  The principal amount of
    Bonds deposited in the Trust per Unit is reflected in the Summary of
    Essential Information.  (See "Organization" in Part B of this Prospectus.) 
    The Units being offered hereby are issued and outstanding Units which have
    been purchased by the Sponsor in the secondary market. 

          INSURANCE.  Each of the Bonds in the Trust is insured by a municipal
    bond guaranty insurance policy obtained by either the Sponsor ("Sponsor-
    Insured Bonds") or the issuers of the Bonds ("Pre-Insured Bonds") and
    issued by one of the insurance companies (the "Insurance Companies"),
    described under "Insurance on the Bonds" in Part B of this Prospectus,
    covering scheduled payment of principal thereof and interest thereon when
    such amounts shall become due for payment but shall not have been paid by
    the issuer or any other insurer thereof.  The insurance, unless obtained
    by Municipal Bond Investors Assurance Corporation ("MBIA Corp."), will
    also cover any accelerated payments of principal and the increase in
    interest payments or premiums, if any, payable upon mandatory redemption
    of the Bonds if interest on any Bonds is ultimately deemed to be subject
    to regular federal income tax.  Insurance obtained from MBIA Corp. only
    guarantees the accelerated payments required to be made by or on behalf of
    an issuer of small industrial revenue bonds and pollution control bonds if
    there is an event which results in the loss of tax-exempt status of the
    interest on such Bonds, including principal, interest or premium payments,
    if any, as and when required.  To the extent, therefore, that Bonds are
    only covered by insurance obtained from MBIA Corp., such Bonds will not be
    covered for the accelerated payments required to be made by or on behalf
    of an issuer of other than small industrial revenue bonds or pollution
    control revenue bonds if there occurs an event which results in the loss
    of tax-exempt status of the interest on such Bonds.  None of the insurance
    will cover accelerated payments of principal or penalty interest or
    premiums unrelated to taxability of interest on the Bonds (although the
    insurance, including insurance obtained by MBIA Corp., does guarantee
    payment of principal and interest in such amounts and at such times as
    such amounts would have been due absent such acceleration).  The insurance
    relates only to the prompt payment of principal of and interest on the
    securities in the portfolio, and does not remove market risks or guarantee
    the market value of the Units in the Trust.  The terms of the insurance
    are more fully described under "Insurance on the Bonds" in Part B of this
    Prospectus.  For a discussion of the effect of an occurrence of nonpayment
    of principal or interest on any Bonds in the Trust, see "Portfolio
    Supervision" in Part B of this Prospectus.  No representation is made
    herein as to any Bond insurer's ability to meet its obligations under a
    policy of insurance relating to any of the Bonds.  In addition, investors
    should be aware that, subsequent to the Date of Deposit, the rating of the
    claims-paying ability of the insurer of an underlying Bond may be
    downgraded, which may result in a downgrading of the rating of the Units
    in the Trust.  The approximate percentage of the aggregate principal
    amount of the portfolio that is insured by each Insurance Company is as
    follows:  AMBAC Indemnity Corp. ("AMBAC"), 24.4%; Bond Investors Guaranty
    ("BIG"), 2.5%; Financial Guaranty Insurance Company ("Financial
    Guaranty"), 16.6%; and Municipal Bond Insurance Association ("MBIA"),
    56.7%. 

          PUBLIC OFFERING PRICE.  The secondary market Public Offering Price
    of each Unit is equal to the aggregate bid price of the Bonds in the Trust
    divided by the number of Units outstanding, plus a sales charge of 5.5% of
    the Public Offering Price, or 5.820% of the net amount invested in Bonds
    per Unit.  In addition, accrued interest to the expected date of
    settlement, including earned original issue discount, is added to the
    Public Offering Price.  If Units had been available for sale on the
    Evaluation Date, the Public Offering Price per Unit would have been
    $472.89 plus accrued interest of $7.91 under the monthly distribution
    plan, $10.86 under the semi-annual distribution plan and $10.82 under the
    annual distribution plan, for a total of $480.80, $483.75 and $483.71,
    respectively.  The Public Offering Price per Unit can vary on a daily
    basis in accordance with fluctuations in the aggregate bid price of the
    Bonds.  (See "Public Offering--Offering Price" in Part B of this
    Prospectus.)

          ESTIMATED LONG TERM RETURN AND ESTIMATED CURRENT RETURN.  The rate
    of return on an investment in Units of the Trust is measured in terms of
    "Estimated Current Return" and "Estimated Long Term Return".

          Estimated Long Term Return is calculated by:  (1) computing the
    yield to maturity or to an earlier call date (whichever results in a lower
    yield) for each Bond in the Trust's portfolio in accordance with accepted
    bond practices, which practices take into account not only the interest
    payable on the Bond but also the amortization of premiums or accretion of
    discounts, if any; (2) calculating the average of the yields for the Bonds
    in the Trust's portfolio by weighing each Bond's yield by the market value
    of the Bond and by the amount of time remaining to the date to which the
    Bond is priced (thus creating an average yield for the portfolio of the
    Trust); and (3) reducing the average yield for the portfolio of the Trust
    in order to reflect estimated fees and expenses of the Trust and the
    maximum sales charge paid by investors.  The resulting Estimated Long Term
    Return represents a measure of the return to investors earned over the
    estimated life of the Trust.  (For the Estimated Long Term Return to
    Certificateholders under the monthly, semi-annual and annual distribution
    plans, see "Summary of Essential Information".)

          Estimated Current Return is a measure of the Trust's cash flow. 
    Estimated Current Return is computed by dividing the Estimated Net Annual
    Interest Income per Unit by the Public Offering Price per Unit.  In
    contrast to the Estimated Long Term Return, the Estimated Current Return
    does not take into account the amortization of premium or accretion of
    discount, if any, on the Bonds in the portfolio of the Trust.  Moreover,
    because interest rates on Bonds purchased at a premium are generally
    higher than current interest rates on newly issued bonds of a similar type
    with comparable rating, the Estimated Current Return per Unit may be
    affected adversely if such Bonds are redeemed prior to their maturity.

          The Estimated Net Annual Interest Income per Unit of the Trust will
    vary with changes in the fees and expenses of the Trustee and the
    Evaluator applicable to the Trust and with the redemption, maturity, sale
    or other disposition of the Bonds in the Trust.  The Public Offering Price
    will vary with changes in the bid prices of the Bonds.  Therefore, there
    is no assurance that the present Estimated Current Return or Estimated
    Long Term Return will be realized in the future.  (For the Estimated
    Current Return to Certificateholders under the monthly, semi-annual and
    annual distribution plans, see "Summary of Essential Information".  See
    "Estimated Long Term Return and Estimated Current Return" in Part B of
    this Prospectus.)

          A schedule of cash flow projections is available from the Sponsor
    upon request.

          DISTRIBUTIONS.  Distributions of interest income, less expenses,
    will be made by the Trust either monthly, semi-annually or annually
    depending upon the plan of distribution applicable to the Unit purchased. 
    A purchaser of a Unit in the secondary market will initially receive
    distributions in accordance with the distribution plan chosen by the prior
    owner of such Unit and may thereafter change the plan as provided under
    "Interest and Principal Distributions" in Part B of this Prospectus. 
    Distributions of principal, if any, will be made semi-annually on June 15
    and December 15 of each year.  (See "Rights of Certificateholders--
    Interest and Principal Distributions" in Part B of this Prospectus.  For
    estimated monthly, semi-annual and annual interest distributions, see
    "Summary of Essential Information.")

          MARKET FOR UNITS.  The Sponsor, although not obligated to do so,
    presently maintains and intends to continue to maintain a secondary market
    for the Units at prices based on the aggregate bid price of the Bonds in
    the Trust portfolio.  The reoffer price will be based on the aggregate bid
    price of the Bonds plus a sales charge of 5.5% of the Public Offering
    Price (5.820% of the net amount invested), plus net accrued interest.  If
    a market is not maintained a Certificateholder will be able to redeem his
    Units with the Trustee at a price also based on the aggregate bid price of
    the Bonds.  (See "Liquidity--Sponsor Repurchase" and "Public Offering--
    Offering Price" in Part B of this Prospectus.)
        
          TOTAL REINVESTMENT PLAN.  Certificateholders under the semi-annual
    and annual plans of distribution have the opportunity to have all their
    regular interest distributions, and principal distributions, if any,
    reinvested in available series of "Insured Municipal Securities Trust" or
    "Municipal Securities Trust."  (See "Total Reinvestment Plan" in Part B of
    this Prospectus.  Residents of Texas see "Total Reinvestment Plan for
    Texas Residents" in Part B of this Prospectus.)  The Plan is not designed
    to be a complete investment program. 


    <PAGE>
       
                        INSURED MUNICIPAL SECURITIES TRUST
                               20TH DISCOUNT SERIES

             SUMMARY OF ESSENTIAL INFORMATION AS OF DECEMBER 31, 1993

    Date of Deposit:  May 29, 1986             Minimum Principal Distribution:
    Principal Amount of Bonds ...$6,040,000     $1.00 per Unit.
    Number of Units .............12,447        Weighted Average Life to
    Fractional Undivided Inter-                Maturity:
      est in Trust per Unit .....1/12447        12.6 Years.
    Principal Amount of                        Minimum Value of Trust:
      Bonds per Unit ............$485.26        Trust may be terminated if
    Secondary Market Public                     value of Trust is less than
      Offering Price**                          $5,000,000 in principal amount
      Aggregate Bid Price                       of Bonds.
        of Bonds in Trust .......$5,562,347+++ Mandatory Termination Date:
      Divided by 12,447 Units ...$446.88        The earlier of December 31,
      Plus Sales Charge of 5.5%                 2035 or the disposition of the
        of Public Offering Price $26.01         last Bond in the Trust.
      Public Offering Price                    Trustee***:  United States Trust 
        per Unit ................$472.89+       Company of New York.
    Redemption and Sponsor's                   Trustee's Annual Fee:  Monthly 
      Repurchase Price                          plan $1.02 per $1,000; semi-
      per Unit ..................$446.88+       annual plan $.54 per $1,000;
                                        +++     and annual plan is $.35 per
                                        ++++    $1,000.
    Excess of Secondary Market                 Evaluator:  Kenny S&P Evaluation
      Public Offering Price                     Services. 
      over Redemption and                      Evaluator's Fee for Each
      Sponsor's Repurchase                      Evaluation:  Minimum of $12
      Price per Unit ............$26.01++++     plus $.25 per each issue of
    Difference between Public                   Bonds in excess of 50 issues
      Offering Price per Unit                   (treating separate maturities
      and Principal Amount per                  as separate issues).
      Unit Premium/(Discount) ...$(12.37)      Sponsor:  Bear, Stearns & Co.
    Evaluation Time:  4:00 p.m.                Inc.
      New York Time.                           Sponsor's Annual Fee:  Maximum of
                                                $.15 per $1,000 principal
                                                amount of Bonds (see "Trust
                                                Expenses and Charges" in Part B
                                                of this Prospectus).

        PER UNIT INFORMATION BASED UPON INTEREST DISTRIBUTION PLAN ELECTED

                                            Monthly   Semi-Annual   Annual
                                            Option      Option      Option


    Gross annual interest income# .........$38.74       $38.74     $38.74
    Less estimated annual fees and
      expenses ............................  1.21          .82        .71
    Estimated net annual interest          ______       ______     ______
      income (cash)# ......................$37.53       $37.92     $38.03
    Estimated interest distribution# ......  3.12        18.96      38.03
    Estimated daily interest accrual# ..... .1042        .1053      .1056
    Estimated current return#++ ........... 7.94%        8.02%      8.04%
    Estimated long term return++ .......... 3.19%        3.28%      3.30%
    Record dates .......................... 1st of      Dec. 1 and  Dec. 1
                                            each month  June 1
    Interest distribution dates ........... 15th of     Dec. 15 and Dec. 15
                                            each month  June 15
        
    <PAGE>
       *  The Date of Deposit is the date on which the Trust Agreement was
          signed and the deposit of the Bonds with the Trustee made.

      **  For information regarding offering price per Unit and applicable
          sales charge under the Total Reinvestment Plan, see "Total
          Reinvestment Plan" in Part B of this Prospectus. 

     ***  The Trustee maintains its corporate trust office at 770 Broadway,
          New York, New York 10003 (tel. no. 1-800-428-8890).  For information
          regarding redemption by the trustee, see "Trustee Redemption" in
          Part B of this Prospectus.
       
       +  Plus accrued interest to the expected date of settlement
          (approximately five business days after purchase) of $7.91 monthly,
          $10.86 semi-annually and $10.82 annually. 
        
      ++  The estimated current return and estimated long term return are
          increased for transactions entitled to a discount (see "Employee
          Discounts" in Part B of this Prospectus), and are higher under the
          semi-annual and annual options due to lower Trustee's fees and
          expenses.

     +++  Based solely upon the bid side evaluation of the underlying Bonds
          (including, where applicable, undistributed cash from the principal
          account).  Upon tender for redemption, the price to be paid will be
          calculated as described under "Trustee Redemption" in Part B of this
          Prospectus. 

    ++++  See "Comparison of Public Offering Price, Sponsor's Repurchase Price
          and Redemption Price" in Part B of this Prospectus. 

       #  Does not include income accrual from original issue discount bonds,
          if any.

    <PAGE>
       
                          INFORMATION REGARDING THE TRUST
                              AS OF DECEMBER 31, 1993


    DESCRIPTION OF PORTFOLIO*

          The portfolio of the Trust consists of 23 issues representing
    obligations of issuers located in 12 states and the District of Columbia. 
    The Sponsor has not participated as a sole underwriter or manager, co-
    manager or member of an underwriting syndicate from which any of the
    initial aggregate principal amount of the Bonds were acquired. 
    Approximately 16.6% of the Bonds are obligations of state and local
    housing authorities; approximately 21.8% are hospital revenue bonds;
    approximately 5.5% were issued in connection with the financing of nuclear
    generating facilities; and none are "mortgage subsidy" bonds.  All of the
    Bonds in the Trust are subject to redemption prior to their stated
    maturity dates pursuant to sinking fund or optional call provisions.  The
    Bonds may also be subject to other calls, which may be permitted or
    required by events which cannot be predicted (such as destruction,
    condemnation, termination of a contract, or receipt of excess or
    unanticipated revenues).  Three of the issues representing $935,000 of the
    principal amount of the Bonds are general obligation bonds.  All 20 of the
    remaining issues representing $5,105,000 of the principal amount of the
    Bonds are payable from the income of a specific project or authority and
    are not supported by the issuer's power to levy taxes.  The portfolio is
    divided for purpose of issue as follows:  Coal Power 1, Federally Insured
    Mortgage 2, Hospital 5, Nuclear Power 2, Pollution Control 2, Sewage
    Disposal 1, Solid Waste 1, Water 2, and Water and Sewer 3.  For an
    explanation of the significance of these factors see "The Trust--
    Portfolio" in Part B of this Prospectus. 


    *     Changes in the Trust Portfolio:  From January 1, 1994 to March 24,
          1994, the entire principal amount of the Bonds in portfolio no. 8
          has been called for redemption pursuant to pre-refunding provisions
          and is no longer contained in the Trust.  The entire principal
          amount of the Bonds in portfolio no. 23 has been called and is no
          longer contained in the Trust.  5 Units have been redeemed from the
          Trust.


          As of December 31, 1993, $1,000,000 (approximately 16.6% of the
    aggregate principal amount of the Bonds) were original issue discount
    bonds.  Of these original issue discount bonds, $1,000,000 (approximately
    16.6% of the aggregate principal amount of the Bonds) were Zero Coupon
    Bonds.  Zero Coupon Bonds do not provide for the payment of any current
    interest and provide for payment at maturity at par value unless sooner
    sold or redeemed.  The market value of Zero Coupon Bonds is subject to
    greater fluctuations than coupon bonds in response to changes in interest
    rates.  Approximately 4.6% of the aggregate principal amount of the Bonds
    in the Trust were purchased at a "market" discount from par value at
    maturity, approximately 78.8% were purchased at a premium and none were
    purchased at par.  For an explanation of the significance of these factors
    see "Discount and Zero Coupon Bonds" in Part B of this Prospectus. 

          None of the Bonds in the Trust are subject to the federal individual
    alternative minimum tax under the Tax Reform Act of 1986.  See "Tax
    Status" in Part B of this Prospectus. 
        
    <PAGE>

                       FINANCIAL AND STATISTICAL INFORMATION


    Selected data for each Unit outstanding for the periods listed below:
       
                                                                    Distribu-
                                                                    tions of
                                          Distributions of Interest Principal
                                          During the Period (per Unit)  During
                               Net Asset *           Semi-             the
                    Units Out-   Value    Monthly   Annual  Annual  Period
    Period Ended     standing  Per Unit   Option    Option  Option (Per Unit)


    December 31, 1991 12,500   $599.61    $46.92   $47.54   $47.73    -0-
    December 31, 1992 12,500    545.79     46.92    47.54    47.73 $41.20
    December 31, 1993 12,447    457.61     40.45    40.97    41.13  71.52


    *     Net Asset Value per Unit is calculated by dividing net assets as
          disclosed in the "Statement of Net Assets" by the number of Units
          outstanding as of the date of the Statement of Net Assets.  See
          Note 5 of Notes to Financial Statements for a description of the
          components of Net Assets.


        
    <PAGE>

Independent Auditors' Report


The Sponsor, Trustee and Certificateholders
Insured Municipal Securities Trust, 20th Discount Series:


We have audited the accompanying statement of net assets, including the
portfolio, of Insured Municipal Securities Trust, 20th Discount Series
as of December 31, 1993, and the related statements of operations, and
changes in net assets for each of the years in the three year period then
ended.  These financial statements are the responsibility of the Trustee
(see note 2).  Our responsibility is to express an opinion on these
financial statements based on our audits.

We conducted our audits in accordance with generally accepted auditing
standards.  Those standards require that we plan and perform the audit to
obtain reasonable assurance about whether the financial statements are
free of material misstatement.  An audit includes examining, on a test
basis, evidence supporting the amounts and disclosures in the financial
statements.  Our procedures included confirmation of securities owned as
of December 31, 1993, by correspondence with the Trustee.  An audit also
includes assessing the accounting principles used and significant
estimates made by management, as well as evaluating the overall financial
statement presentation.  We believe that our audits provide a reasonable
basis for our opinion.

In our opinion, the financial statements referred to above present
fairly, in all material respects, the financial position of Insured
Municipal Securities Trust, 20th Discount Series as of December 31,
1993, and the results of its operations and the changes in its net
assets for each of the years in the three year period then ended in
conformity with generally accepted accounting principles.



    KPMG Peat Marwick


New York, New York
March 31, 1994
<PAGE>


                              Statement of Net Assets
                        
                                 December 31, 1993 
                        
  Investments in marketable securities,
     at market value (cost  $5,696,339)                   $  5,562,336

  Excess of other assets over total liabilities                133,481
                                                            -----------

  Net assets 12,447 units of fractional undivided
     interest outstanding, $457.61 per  unit)             $  5,695,817
                                                            ===========
                     
  See accompanying notes to financial statements.

<PAGE>
<TABLE>
                              Statements of Operations
<CAPTION>
                                                     Years ended December 31,      
                                             ---------- --- ---------- ---  ---------
                                                1993           1992           1991 
                                             ----------     ----------      ---------
<S>                                       <C>               <C>             <C>
     Investment income - interest         $    526,573        621,312        622,087
                                             ----------     ----------      ---------

     Expenses:          
        Trustee's fees                          10,341         11,935         10,461
        Evaluator's fees                         3,558          3,288          2,772
        Sponsor's advisory fee                   1,565          1,652          1,652
                                             ----------     ----------      ---------

                Total expenses                  15,464         16,875         14,885
                                             ----------     ----------      ---------

                Investment income, net         511,109        604,437        607,202
                                             ----------     ----------      ---------

     Realized and unrealized gain                       
       (loss) on investments:                           
          Net realized loss on                          
            bonds sold or called              (115,382)       (39,565)          -  
          Unrealized appreciation                       
           (depreciation) for the year         (95,953)      (133,116)       154,245
                                             ----------     ----------      ---------

                Net gain (loss)                         
                  on investments              (211,335)      (172,681)       154,245
                                             ----------     ----------      ---------

                Net increase in net                     
                  assets resulting                      
                  from operations         $    299,774        431,756        761,447
                                             ==========     ==========      =========

See accompanying notes to financial statements.
</TABLE>
<PAGE>

<TABLE>
                         Statements of Changes in Net Assets

<CAPTION>
                                                          Years ended December 31,
                                               ---------------------------------------------
                                                   1993             1992            1991 
                                               -------------     -----------     -----------
<S>                                         <C>                  <C>             <C>
    Operations:               
       Investment income, net                $      511,109         604,437         607,202
       Net realized loss on   
         bonds sold or called                      (115,382)        (39,565)          -  
       Unrealized appreciation
         (depreciation) for the year                (95,953)       (133,116)        154,245
                                               -------------     -----------     -----------
   
                  Net increase in net                         
                     assets resulting                         
                     from operations                299,774         431,756         761,447
                                               -------------     -----------     -----------
   
    Distributions to Certificateholders:                      
         Investment income                          507,565         589,540         589,694
         Principal                                  892,699         515,000           -  
    Redemptions:              
        Interest                                        620           -               -  
        Principal                                    25,441           -               -  
                                               -------------     -----------     -----------
   
                  Total distributions                         
                    and redemptions               1,426,325       1,104,540         589,694
                                               -------------     -----------     -----------
   
                  Total increase (decrease)      (1,126,551)       (672,784)        171,753
   
    Net assets at beginning of year               6,822,368       7,495,152       7,323,399
                                               -------------     -----------     -----------
   
    Net assets at end of year (including                      
       undistributed net investment                           
       income of  $154,628,  $220,599 and                     
       $205,702 respectively)                $    5,695,817       6,822,368       7,495,152
                                               =============     ===========     ===========

See accompanying notes to financial statements.
</TABLE>
<PAGE>

Notes to Financial Statements

December 31, 1993, 1992 and 1991

(1)    Organization

Insured Municipal Securities Trust, 20th Discount Series (Trust) was
organized on May 29, 1986 by Bear, Stearns & Co. Inc. (Sponsor) under
the laws of the State of New York by a Trust Indenture and Agreement,
and is registered under the Investment Company Act of 1940.

(2)    Summary of Significant Accounting Policies

United States Trust Company of New York (Trustee) has custody of and
responsibility for the accounting records and financial statements of
the Trust and is responsible for establishing and maintaining a
system of internal control related thereto.

The Trustee is also responsible for all estimates of expenses and
accruals reflected in the Trust's financial statements.  The
accompanying financial statements have been adjusted to record the
unrealized appreciation (depreciation) of investments and to record
interest income and expenses on the accrual basis.

The discount on the zero-coupon bonds is accreted by the interest
method over the respective lives of the bonds.  The accretion of such
discount is included in interest income; however, it is not
distributed until realized in cash upon maturity or sale of the
respective bonds.

Investments are carried at market value which is determined by either
Standard & Poor's Corporation or Moody's Investors Service, Inc.
(Evaluator) as discussed in Footnotes to Portfolio.  The market value
of the investments is based upon the bid prices for the bonds at the
end of the period, except that the market value on the date of deposit
represents the cost to the Trust based on the offering prices for
investments at that date.  The difference between cost (including
accumulated accretion of original issue discount on zero-coupon bonds)
and market value is reflected as unrealized appreciation (depreciation) of
investments.  Securities transactions are recorded on the trade date.
Realized gains (losses) from securities transactions are determined on the
basis of average cost of the securities sold or redeemed.

(3)    Income Taxes

The Trust is not subject to Federal income taxes as provided for by
the Internal Revenue Code.

(4)    Trust Administration

The fees and expenses of the Trust are incurred and paid on the basis
set forth under "Trust Expenses and Charges" in Part B of this
Prospectus.

The Trust Indenture and Agreement provides for interest distributions
as often as monthly (depending upon the distribution plan elected by
the Certificateholders).

The Trust Indenture and Agreement further requires that principal
received from the disposition of bonds, other than those bonds sold
in connection with the redemption of units, be distributed to
Certificateholders.

See "Financial and Statistical Information" in Part A of this
Prospectus for the amounts of per unit distributions during the years
ended December 31, 1993, 1992, and 1991.

The Trust Indenture and Agreement also requires the Trust to redeem
units tendered.  53 units were redeemed by the Trust during the year
ended December 31, 1993.  No units were redeemed during the years
ended December 31, 1992 and 1991.

(5)    Net Assets

At December 31, 1993, the net assets of the Trust represented the
interest of Certificateholders as follows:

   Original cost to Certificateholders                   $ 7,687,523
   Less initial gross underwriting commission               (422,750)
                                                           7,264,773

   Cost of securities sold or called                      (1,589,592)
   Net unrealized depreciation                              (134,003)
   Undistributed net investment income                       154,628
   Undistributed proceeds from bonds sold or called               11

                              Total                      $ 5,695,817


The original cost to Certificateholders, less the initial gross
underwriting commission, represents the aggregate initial public
offering price net of the applicable sales charge on 12,500 units
fractional undivided interest of the Trust as of the date of deposit.

Undistributed net investment income includes accumulated accretion of
original issue discount of $21,158.

<PAGE>

<TABLE>
INSURED MUNICIPAL SECURITIES TRUST, 20TH DISCOUNT SERIES

  Portfolio                
 December 31, 1993         

<CAPTION>

Port-   Aggregate                                   Coupon Rate/   Redemption Feature
folio   Principal       Name of Issuer     Ratings  Date(s) of     S.F.--Sinking Fund        Market
No.      Amount       and Title of Bonds     (1)    Maturity(2)    Ref.--Refunding(2)(7)    Value(3)
- ----    ---------    ---------------------   ----   ------------   --------------------     ---------
<S>   <C>            <C>                     <C>    <C>            <C>                   <C>
 1    $   200,000    City of Ft. Smith,      AAA    9.750%         2/01/06 @ 100 S.F.    $    218,842
                     Arkansas Water and             2/01/2015      2/01/95 @ 102.5 Ref.            
                     Sewer Revenue Bonds,
                     1985 Series (MBIA) 
                     (5)                
             
             
             
 2        500,000    Hillsboro County,       AAA    10.500         10/01/03 @ 100 S.F.        536,845
                     Florida Solid Waste            10/01/2008     10/01/94 @ 102 Ref.             
                     and Resource Recovery
                     Revenue Bonds, 1984
                     Series A (MBIA)    
             
             
 3a        60,000    City of Niceville,      AAA    8.875          No Sinking Fund             66,080
                     Florida Water and              6/01/2010      6/01/95 @ 103 Ref.              
                     Sewer Revenue Bonds,
                     1985 Series        
                     (Financial Guaranty)
             
 3b        40,000    City of Niceville,      AAA    8.875          No Sinking Fund             44,312
                     Florida Water and              6/01/2010      6/01/95 @ 103 Ref.              
                     Sewer Revenue Bonds,
                     1985 Series        
                     (Financial Guaranty)
                     (5)                
             
             
 4         60,000    Municipal Electric      AAA    9.000          1/01/08 @ 100 S.F.          64,345
                     Authority of Georgia           1/01/2020      1/01/95 @ 102 Ref.              
                     Power Revenue Bonds,
                     1985 Series K (AMBAC)
             
 5        500,000    Development Authority   AAA    11.625         No Sinking Fund            537,500
                     of Burke County                9/01/2014      9/01/94 @ 102 Ref.              
                     (Georgia) Pollution
                     Control Revenue    
                     Bonds, (Georgia Power
                     Company Plant Vogtle
                     Project) 1984 Series
                     2 (Financial       
                     Guaranty)          
             
 6         75,000    Northwest Suburban      AAA    9.875          5/01/08 @ 100 S.F.          82,280
                     Municipal Joint                5/01/2013      5/01/95 @ 101 Ref.              
                     Action Water Agency
                     (Cook, Du Page and 
                     Kane Counties,     
                     Illinois) Water    
                     Supply System Revenue
                     Bonds, 1985 Series 
                     (MBIA) (5)         
             
 7        150,000    The Hospital            AAA    9.125          7/01/01 @ 100 S.F.         165,962
                     Authority of the City          7/01/2015      7/01/95 @ 102 Ref.              
                     of Fort Wayne,     
                     Indiana Hospital   
                     Revenue Refunding  
                     Bonds (Ancilla     
                     Systems Incorported)
                     1985 Series A (BIG)
                     (5)                
             
 8        300,000    Jasper County Indiana   AAA    10.000         3/01/07 @ 100 S.F.         309,795
                     Hospital Authority             3/01/2009      3/01/94 @ 102 Ref.              
                     Hospital Facility  
                     Revenue Memorial   
                     Hospital and Health
                     Care Center Project
                     1984 Series (MBIA) 
                     (5)                
             
             
             
 9         30,000    City of Detroit,        AAA    10.625%        12/15/95 @ 100 S.F.         32,976
                     Michigan Sewage                12/15/2009     12/15/94 @ 103 Ref.             
                     Disposal System    
                     Revenue Bonds, 1984
                     Series (AMBAC) (5) 
             
                          See           
10        500,000    County of Monroe,       AAA    9.625          12/01/96 @ 100 S.F.        569,925
                     Michigan Pollution             12/01/2015     12/01/95 @ 103 Ref.             
                     Control Revenue Bonds
                     (Detroit Edison    
                     Company Project) 1985
                     Series A(AMBAC)    
             
11        500,000    City of Albuquerque,    AAA    9.250          8/01/05 @ 100 S.F.         553,565
                     New Mexico Hospital            8/01/2012      8/01/95 @ 102 Ref.              
                     System Revenue     
                     Refunding Bonds    
                     Southwest Community
                     Health Service     
                     Project 1985 Series B
                     (MBIA)             
             
12        275,000    North Carolina          AAA    6.500          7/01/21 @ 100 S.F.         282,381
                     Eastern Municipal              1/01/2024      1/01/95 @ 100 Ref.              
                     Power Agency Power 
                     System Revenue Bonds,
                     1985 Series E (AMBAC)
             
13        250,000    Lycoming County,        AAA    9.375          11/01/01 @ 100 S.F.        282,358
                     Pennsylvania Hospital          11/01/2015     11/01/95 @ 102 Ref.             
                     Authority, Hospital
                     Lease Revenue Bonds,
                     1985 Series        
                     (Williamsport      
                     Hospital Project)  
                     (AMBAC) (5)        
             
14        100,000    Rhode Island Health     AAA    9.375          7/01/08 @ 100 S.F.         111,006
                     and Educational                7/01/2012      7/01/95 @ 102 Ref.              
                     Building Corporation
                     Hospital Financing 
                     Revenue Bonds The  
                     Memorial Hospital  
                     Issue 1985 Series  
                     (MBIA) (5)         
             
15        400,000    City of Beaumont,       AAA    9.000          9/01/02 @ 100 S.F.         437,536
                     Texas Limited Tax              9/01/2005      9/01/95 @ 100 Ref.              
                     General Obligation 
                     Bonds, 1985 Series 
                     (Financial Guaranty)
                     (5)                
             
16        250,000    Galveston County        AAA    8.875          7/10/01 @ 100 S.F.         282,458
                     (Texas) Water                  7/10/2005      7/10/96 @ 100 Ref.              
                     Authority Water    
                     Systems Contract   
                     Revenue Refunding  
                     Bonds-Mainland     
                     Project 1985 Series
                     (AMBAC) (5)        
             
17        115,000    Henderson County,       AAA    10.250         9/01/05 @ 100 S.F.         122,570
                     Texas Hospital                 9/01/2014      9/01/94 @ 102 Ref.              
                     Authority East     
                     Regional Health    
                     Facility Project 1984
                     Series (MBIA) (5)  
             
             
18        100,000    Park Ten (Texas)        AAA    9.800%         No Sinking Fund            107,526
                     Municipal Utility              3/01/2002      3/01/95 @ 100 Ref.              
                     District, Waterworks
                     and Sewer System   
                     Revenue Bonds, 1983
                     Series (MBIA) (5)  
             
 19       250,000    Pecan Grove Municipal   AAA    8.700          No Sinking Fund            300,718
                     Utility District (A            9/01/2002      9/01/99 @ 100 Ref.              
                     Political Subdivision
                     Located in Fort Bend
                     County, Texas)     
                     Unlimited Tax Bonds,
                     1985 Series  (MBIA)
             
                          See           
20        285,000    City of Waxahachie,     AAA    9.600          No Sinking Fund            304,349
                     Texas (Ellis County)           2/01/2001      2/01/95 @ 100 Ref.              
                     General Obligation 
                     Bonds, 1985 Series 
                     (MBIA) (5)         
             
21        100,000    Intermountain Power     AAA    9.625          7/01/06 @ 100 S.F.         111,847
                     Agency (A Political            7/01/2008      7/01/95 @ 102.5 Ref.            
                     Subdivision of the 
                     State of Utah) Power
                     Supply Revenue     
                     Refunding Bonds, 1985
                     Series A (AMBAC) (5)
             
22        500,000    The District of         AAA    0.000          5/01/05 @ 11.975 S.F.       20,115
                     Columbia Multi-Unit            11/01/2025     11/01/98 @ 6.415 Ref.           
                     Housing Finance    
                     Corporation Mortgage
                     Revenue Bonds, 1983
                     Series  (FHA Insured
                     Mortgage           
                     Loan-Congress Park II
                     Apartments Section 8
                     Assisted Project)  
                     (MBIA)             
             
23        500,000    Anne Arundel County,    AAA    0.000          6/01/21 @ 54.504 S.F.       17,045
                     Maryland Economic              6/01/2027      1/06/94 @ 3.409 Ref.            
                     Development Revenue
                     Bonds, 1985 Series 
                     (FHA Insured Mortgage
                     Loan-The Regency Club
                     II Facility) (MBIA)
             
        ---------                                                                           ---------
      $ 6,040,000                                                                        $  5,562,336
        =========                                                                           =========

 See accompanying footnotes to portfolio and notes to financial statements.
</TABLE>

<PAGE>
Footnotes to Portfolio

December 31, 1993

(1) All ratings are by Standard & Poor's Corporation.  A brief
description of the ratings symbols and their meanings is set forth
under "Description of Bond Ratings" in Part B of this Prospectus.

(2)  See "The Trust - Portfolio" in Part B of this Prospectus for an
explanation of redemption features.  See "Tax Status" in Part B of
this Prospectus for a statement of the Federal tax consequences to a
Certificateholder upon the sale, redemption or maturity of a bond.

(3) At December 31, 1993, the net unrealized depreciation of all the
bonds was comprised of the following:

    Gross unrealized appreciation                  $  97,471
    Gross unrealized depreciation                   (231,474)

    Net unrealized depreciation                    $ (134,003)

(4) The annual interest income, based upon bonds held at December 31,
1993, (excluding accretion of original issue discount on zero-coupon
bonds) to the Trust is $482,253.

(5) The bonds have been prerefunded and will be redeemed at the next
refunding call date.

(6)  Bonds sold or called after December 31, 1993 are noted in a footnote
"Changes in Trust Portfolio" under "Description of Portfolio" in Part
A of this Prospectus.

(7) The Bonds may also be subject to other calls, which may be permitted
or required by events which cannot be predicted (such as destruction,
condemnation, termination of a contract, or receipt of excess or
unanticipated revenues).
<PAGE>


                 NOTE:  Part A of This Prospectus May Not Be     
                        Distributed Unless Accompanied by Part B.


                        INSURED MUNICIPAL SECURITIES TRUST

                               21ST DISCOUNT SERIES
                              (MULTIPLIER PORTFOLIO)


                                                                              
       
          The Trust is a unit investment trust designated 21st Discount Series
    ("Insured Municipal Discount Trust") with an underlying portfolio of long-
    term insured tax-exempt bonds issued by or on behalf of states,
    municipalities and public authorities and was formed to preserve capital
    and to provide interest income (including, where applicable, earned
    original issue discount) which, in the opinions of bond counsel to the
    respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law but may be subject to state
    and local taxes.  Capital gains are subject to tax.  (See "Tax Status" and
    "The Trust--Portfolio" in Part B of this Prospectus.)  The Sponsor is
    Bear, Stearns & Co. Inc.  The value of the Units of the Trust will
    fluctuate with the value of the underlying bonds.  Minimum purchase:  1
    Unit. 

                                                                              


          This Prospectus consists of two parts.  Part A contains the Summary
    of Essential Information as of December 31, 1993 (the "Evaluation Date"),
    a summary of certain specific information regarding the Trust and audited
    financial statements of the Trust, including the related portfolio, as of
    the Evaluation Date.  Part B of this Prospectus contains a general summary
    of the Trust. 
        
                    Investors should retain both parts of this
                         Prospectus for future reference. 

                                                                              


     THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES
     AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE
     COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR
     ADEQUACY OF THIS PROSPECTUS.  ANY REPRESENTATION TO THE CONTRARY IS A
     CRIMINAL OFFENSE.

       
                      Prospectus Part A Dated April 29, 1994
        



    <PAGE>
       
          THE TRUST.  The Trust is a unit investment trust formed to preserve
    capital and to provide interest income (including, where applicable,
    earned original issue discount) which, in the opinions of bond counsel to
    the respective issuers, is, with certain exceptions, currently exempt from
    regular federal income tax under existing law through investment in a
    fixed, diversified portfolio of long-term insured bonds (the "Bonds")
    issued by or on behalf of states, municipalities and public authorities
    which, because of irrevocable insurance, are rated "AAA" by Standard &
    Poor's Corporation.  Although the Supreme Court has determined that
    Congress has the authority to subject interest on bonds such as the Bonds
    in the Trust to regular federal income taxation, existing law excludes
    such interest from regular federal income tax.  Such interest income may,
    however, be subject to the federal corporate alternative minimum tax and
    to state and local taxes.  (See "Tax Status" in Part B of this
    Prospectus.)  For a list of ratings on the Evaluation Date, see
    "Portfolio."  The Bonds were acquired at prices which resulted in the
    portfolio as a whole being purchased at a deep discount from par value. 
    The portfolio may also include bonds issued at an original issue discount. 
    Additionally, some of the Bonds in the portfolio may be "Zero Coupon
    Bonds," which are original issue discount bonds that provide for payment
    at maturity at par value, but do not provide for the payment of any
    current interest.  Some of the Bonds in the Trust have been issued with
    optional refunding or refinancing provisions ("Refunded Bonds") whereby
    the issuer of the Bond has the right to call such Bond prior to its stated
    maturity date (and other than pursuant to sinking fund provisions) and to
    issue new bonds ("Refunding Bonds") in order to finance the redemption. 
    Issuers typically utilize refunding calls in order to take advantage of
    lower interest rates in the marketplace.  Some of these Refunded Bonds may
    be called for redemption pursuant to pre-refunding provisions ("Pre-
    Refunded Bonds") whereby the proceeds from the issue of the Refunding
    Bonds are typically invested in government securities in escrow for the
    benefit of the holders of the Pre-Refunded Bonds until the refunding call
    date.  Usually, Pre-Refunded Bonds will bear a triple-A rating because of
    this escrow.  The issuers of Pre-Refunded Bonds must call such Bonds on
    their refunding call date.  Therefore, as of such date, the Trust will
    receive the call price for such bonds but will cease receiving interest
    income with respect to them.  For a list of those Bonds which are Pre-
    Refunded Bonds, if any, as of the Evaluation Date, see "Notes to Financial
    Statements" in this Part A.  Some of the Bonds in the portfolio may have
    been purchased at an aggregate premium over par.  All of the Bonds in the
    Trust were rated "AAA" by Standard & Poor's Corporation at the time
    originally deposited in the Trust.  This rating results from insurance
    relating only to the Bonds in the Trust and not to the Units of the Trust. 
    The insurance does not remove market risk, as it does not guarantee the
    market value of the Units.  For a discussion of the significance of such
    ratings, see "Description of Bond Ratings" in Part B of this Prospectus,
    and for a list of ratings on the Evaluation Date see the "Portfolio."  The
    payment of interest and preservation of capital are, of course, dependent
    upon the continuing ability of issuers of the Bonds or the insurers
    thereof to meet their obligations.  There can be no assurance that the
    Trust's investment objectives will be achieved.  Investment in the Trust
    should be made with an understanding of the risks which an investment in
    long-term fixed rate debt obligations may entail, including the risk that
    the value of the underlying portfolio will decline with increases in
    interest rates, and that the value of Zero Coupon Bonds is subject to
    greater fluctuation than coupon bonds in response to changes in interest
    rates.  Each Unit in the Trust represents a 1/11000th undivided interest
    in the principal and net income of the Trust.  The principal amount of
    Bonds deposited in the Trust per Unit is reflected in the Summary of
    Essential Information.  (See "Organization" in Part B of this Prospectus.) 
    The Units being offered hereby are issued and outstanding Units which have
    been purchased by the Sponsor in the secondary market. 

          INSURANCE.  Each of the Bonds in the Trust is insured by a municipal
    bond guaranty insurance policy obtained by either the Sponsor ("Sponsor-
    Insured Bonds") or the issuers of the Bonds ("Pre-Insured Bonds") and
    issued by one of the insurance companies (the "Insurance Companies"),
    described under "Insurance on the Bonds" in Part B of this Prospectus,
    covering scheduled payment of principal thereof and interest thereon when
    such amounts shall become due for payment but shall not have been paid by
    the issuer or any other insurer thereof.  The insurance, unless obtained
    by Municipal Bond Investors Assurance Corporation ("MBIA Corp."), will
    also cover any accelerated payments of principal and the increase in
    interest payments or premiums, if any, payable upon mandatory redemption
    of the Bonds if interest on any Bonds is ultimately deemed to be subject
    to regular federal income tax.  Insurance obtained from MBIA Corp. only
    guarantees the accelerated payments required to be made by or on behalf of
    an issuer of small industrial revenue bonds and pollution control bonds if
    there is an event which results in the loss of tax-exempt status of the
    interest on such Bonds, including principal, interest or premium payments,
    if any, as and when required.  To the extent, therefore, that Bonds are
    only covered by insurance obtained from MBIA Corp., such Bonds will not be
    covered for the accelerated payments required to be made by or on behalf
    of an issuer of other than small industrial revenue bonds or pollution
    control revenue bonds if there occurs an event which results in the loss
    of tax-exempt status of the interest on such Bonds.  None of the insurance
    will cover accelerated payments of principal or penalty interest or
    premiums unrelated to taxability of interest on the Bonds (although the
    insurance, including insurance obtained by MBIA Corp., does guarantee
    payment of principal and interest in such amounts and at such times as
    such amounts would have been due absent such acceleration).  The insurance
    relates only to the prompt payment of principal of and interest on the
    securities in the portfolio, and does not remove market risks or guarantee
    the market value of the Units in the Trust.  The terms of the insurance
    are more fully described under "Insurance on the Bonds" in Part B of this
    Prospectus.  For a discussion of the effect of an occurrence of nonpayment
    of principal or interest on any Bonds in the Trust, see "Portfolio
    Supervision" in Part B of this Prospectus.  No representation is made
    herein as to any Bond insurer's ability to meet its obligations under a
    policy of insurance relating to any of the Bonds.  In addition, investors
    should be aware that, subsequent to the Date of Deposit, the rating of the
    claims-paying ability of the insurer of an underlying Bond may be
    downgraded, which may result in a downgrading of the rating of the Units
    in the Trust.  The approximate percentage of the aggregate principal
    amount of the portfolio that is insured by each Insurance Company is as
    follows:  AMBAC Indemnity Corp. ("AMBAC"), 15.2%; Bond Investors Guaranty
    ("BIG"), 8.5%; Financial Guaranty Insurance Company ("Financial
    Guaranty"), 21.2%; and Municipal Bond Insurance Association ("MBIA"),
    55.2%. 

          PUBLIC OFFERING PRICE.  The secondary market Public Offering Price
    of each Unit is equal to the aggregate bid price of the Bonds in the Trust
    divided by the number of Units outstanding, plus a sales charge of 5.5% of
    the Public Offering Price, or 5.820% of the net amount invested in Bonds
    per Unit.  In addition, accrued interest to the expected date of
    settlement, including earned original issue discount, is added to the
    Public Offering Price.  If Units had been available for sale on the
    Evaluation Date, the Public Offering Price per Unit would have been
    $570.94 plus accrued interest of $7.88 under the monthly distribution
    plan, $11.20 under the semi-annual distribution plan and $11.23 under the
    annual distribution plan, for a total of $578.82, $582.14 and $582.17,
    respectively.  The Public Offering Price per Unit can vary on a daily
    basis in accordance with fluctuations in the aggregate bid price of the
    Bonds.  (See "Public Offering--Offering Price" in Part B of this
    Prospectus.)

          ESTIMATED LONG TERM RETURN AND ESTIMATED CURRENT RETURN.  The rate
    of return on an investment in Units of the Trust is measured in terms of
    "Estimated Current Return" and "Estimated Long Term Return".

          Estimated Long Term Return is calculated by:  (1) computing the
    yield to maturity or to an earlier call date (whichever results in a lower
    yield) for each Bond in the Trust's portfolio in accordance with accepted
    bond practices, which practices take into account not only the interest
    payable on the Bond but also the amortization of premiums or accretion of
    discounts, if any; (2) calculating the average of the yields for the Bonds
    in the Trust's portfolio by weighing each Bond's yield by the market value
    of the Bond and by the amount of time remaining to the date to which the
    Bond is priced (thus creating an average yield for the portfolio of the
    Trust); and (3) reducing the average yield for the portfolio of the Trust
    in order to reflect estimated fees and expenses of the Trust and the
    maximum sales charge paid by investors.  The resulting Estimated Long Term
    Return represents a measure of the return to investors earned over the
    estimated life of the Trust.  (For the Estimated Long Term Return to
    Certificateholders under the monthly, semi-annual and annual distribution
    plans, see "Summary of Essential Information".)

          Estimated Current Return is a measure of the Trust's cash flow. 
    Estimated Current Return is computed by dividing the Estimated Net Annual
    Interest Income per Unit by the Public Offering Price per Unit.  In
    contrast to the Estimated Long Term Return, the Estimated Current Return
    does not take into account the amortization of premium or accretion of
    discount, if any, on the Bonds in the portfolio of the Trust.  Moreover,
    because interest rates on Bonds purchased at a premium are generally
    higher than current interest rates on newly issued bonds of a similar type
    with comparable rating, the Estimated Current Return per Unit may be
    affected adversely if such Bonds are redeemed prior to their maturity.

          The Estimated Net Annual Interest Income per Unit of the Trust will
    vary with changes in the fees and expenses of the Trustee and the
    Evaluator applicable to the Trust and with the redemption, maturity, sale
    or other disposition of the Bonds in the Trust.  The Public Offering Price
    will vary with changes in the bid prices of the Bonds.  Therefore, there
    is no assurance that the present Estimated Current Return or Estimated
    Long Term Return will be realized in the future.  (For the Estimated
    Current Return to Certificateholders under the monthly, semi-annual and
    annual distribution plans, see "Summary of Essential Information".  See
    "Estimated Long Term Return and Estimated Current Return" in Part B of
    this Prospectus.)

          A schedule of cash flow projections is available from the Sponsor
    upon request.

          DISTRIBUTIONS.  Distributions of interest income, less expenses,
    will be made by the Trust either monthly, semi-annually or annually
    depending upon the plan of distribution applicable to the Unit purchased. 
    A purchaser of a Unit in the secondary market will initially receive
    distributions in accordance with the distribution plan chosen by the prior
    owner of such Unit and may thereafter change the plan as provided under
    "Interest and Principal Distributions" in Part B of this Prospectus. 
    Distributions of principal, if any, will be made semi-annually on June 15
    and December 15 of each year.  (See "Rights of Certificateholders--
    Interest and Principal Distributions" in Part B of this Prospectus.  For
    estimated monthly, semi-annual and annual interest distributions, see
    "Summary of Essential Information.")

          MARKET FOR UNITS.  The Sponsor, although not obligated to do so,
    presently maintains and intends to continue to maintain a secondary market
    for the Units at prices based on the aggregate bid price of the Bonds in
    the Trust portfolio.  The reoffer price will be based on the aggregate bid
    price of the Bonds plus a sales charge of 5.5% of the Public Offering
    Price (5.820% of the net amount invested), plus net accrued interest.  If
    a market is not maintained a Certificateholder will be able to redeem his
    Units with the Trustee at a price also based on the aggregate bid price of
    the Bonds.  (See "Liquidity--Sponsor Repurchase" and "Public Offering--
    Offering Price" in Part B of this Prospectus.)
        
          TOTAL REINVESTMENT PLAN.  Certificateholders under the semi-annual
    and annual plans of distribution have the opportunity to have all their
    regular interest distributions, and principal distributions, if any,
    reinvested in available series of "Insured Municipal Securities Trust" or
    "Municipal Securities Trust."  (See "Total Reinvestment Plan" in Part B of
    this Prospectus.  Residents of Texas see "Total Reinvestment Plan for
    Texas Residents" in Part B of this Prospectus.)  The Plan is not designed
    to be a complete investment program. 


    <PAGE>
       
                        INSURED MUNICIPAL SECURITIES TRUST
                               21ST DISCOUNT SERIES

             SUMMARY OF ESSENTIAL INFORMATION AS OF DECEMBER 31, 1993

    Date of Deposit:  June 25, 1986            Minimum Principal Distribution:
    Principal Amount of Bonds ...$8,955,000     $1.00 per Unit.
    Number of Units .............11,000        Weighted Average Life to
    Fractional Undivided Inter-                Maturity:
      est in Trust per Unit .....1/11000        20.2 Years.
    Principal Amount of                        Minimum Value of Trust:
      Bonds per Unit ............$814.09        Trust may be terminated if
    Secondary Market Public                     value of Trust is less than
      Offering Price**                          $4,400,000 in principal amount
      Aggregate Bid Price                       of Bonds.
        of Bonds in Trust .......$5,934,968+++ Mandatory Termination Date:
      Divided by 11,000 Units ...$539.54        The earlier of December 31,
      Plus Sales Charge of 5.5%                 2035 or the disposition of the
        of Public Offering Price $31.40         last Bond in the Trust.
      Public Offering Price                    Trustee***:  United States Trust 
        per Unit ................$570.94+       Company of New York.
    Redemption and Sponsor's                   Trustee's Annual Fee:  Monthly 
      Repurchase Price                          plan $1.02 per $1,000; semi-
      per Unit ..................$539.54+       annual plan $.54 per $1,000;
                                        +++     and annual plan is $.35 per
                                        ++++    $1,000.
    Excess of Secondary Market                 Evaluator:  Kenny S&P Evaluation
      Public Offering Price                     Services. 
      over Redemption and                      Evaluator's Fee for Each
      Sponsor's Repurchase                      Evaluation:  Minimum of $12
      Price per Unit ............$31.40++++     plus $.25 per each issue of
    Difference between Public                   Bonds in excess of 50 issues
      Offering Price per Unit                   (treating separate maturities
      and Principal Amount per                  as separate issues).
      Unit Premium/(Discount) ...$(243.15)     Sponsor:  Bear, Stearns & Co.
    Evaluation Time:  4:00 p.m.                Inc.
      New York Time.                           Sponsor's Annual Fee:  Maximum of
                                                $.15 per $1,000 principal
                                                amount of Bonds (see "Trust
                                                Expenses and Charges" in Part B
                                                of this Prospectus).

        PER UNIT INFORMATION BASED UPON INTEREST DISTRIBUTION PLAN ELECTED

                                            Monthly   Semi-Annual   Annual
                                            Option      Option      Option

    Gross annual interest income# .........$45.18       $45.18     $45.18
    Less estimated annual fees and
      expenses ............................  1.60         1.06        .88
    Estimated net annual interest          ______       ______     ______
      income (cash)# ......................$43.58       $44.12     $44.30
    Estimated interest distribution# ......  3.63        22.06      44.30
    Estimated daily interest accrual# ..... .1210        .1225      .1230
    Estimated current return#++ ........... 7.63%        7.73%      7.76%
    Estimated long term return++ .......... 3.77%        3.86%      3.89%
    Record dates .......................... 1st of      Dec. 1 and  Dec. 1
                                            each month  June 1
    Interest distribution dates ........... 15th of     Dec. 15 and Dec. 15
                                            each month  June 15
    
    
   
    <PAGE>
       *  The Date of Deposit is the date on which the Trust Agreement was
          signed and the deposit of the Bonds with the Trustee made.

      **  For information regarding offering price per Unit and applicable
          sales charge under the Total Reinvestment Plan, see "Total
          Reinvestment Plan" in Part B of this Prospectus. 

     ***  The Trustee maintains its corporate trust office at 770 Broadway,
          New York, New York 10003 (tel. no. 1-800-428-8890).  For information
          regarding redemption by the trustee, see "Trustee Redemption" in
          Part B of this Prospectus.
        
       +  Plus accrued interest to the expected date of settlement
          (approximately five business days after purchase) of $7.88 monthly,
          $11.20 semi-annually and $11.23 annually. 
       
      ++  The estimated current return and estimated long term return are
          increased for transactions entitled to a discount (see "Employee
          Discounts" in Part B of this Prospectus), and are higher under the
          semi-annual and annual options due to lower Trustee's fees and
          expenses.

     +++  Based solely upon the bid side evaluation of the underlying Bonds
          (including, where applicable, undistributed cash from the principal
          account).  Upon tender for redemption, the price to be paid will be
          calculated as described under "Trustee Redemption" in Part B of this
          Prospectus. 

    ++++  See "Comparison of Public Offering Price, Sponsor's Repurchase Price
          and Redemption Price" in Part B of this Prospectus. 

       #  Does not include income accrual from original issue discount bonds,
          if any.

    <PAGE>
    
    
   
                          INFORMATION REGARDING THE TRUST
                              AS OF DECEMBER 31, 1993


    DESCRIPTION OF PORTFOLIO

          The portfolio of the Trust consists of 30 issues representing
    obligations of issuers located in 12 states and the District of Columbia. 
    The Sponsor has not participated as a sole underwriter or manager, co-
    manager or member of an underwriting syndicate from which any of the
    initial aggregate principal amount of the Bonds were acquired. 
    Approximately 47.3% of the Bonds are obligations of state and local
    housing authorities; approximately 5.6% are hospital revenue bonds;
    approximately 7.3% were issued in connection with the financing of nuclear
    generating facilities; and none are "mortgage subsidy" bonds.  All of the
    Bonds in the Trust are subject to redemption prior to their stated
    maturity dates pursuant to sinking fund or optional call provisions.  The
    Bonds may also be subject to other calls, which may be permitted or
    required by events which cannot be predicted (such as destruction,
    condemnation, termination of a contract, or receipt of excess or
    unanticipated revenues).  Four of the issues representing $685,000 of the
    principal amount of the Bonds are general obligation bonds.  All 26 of the
    remaining issues representing $8,270,000 of the principal amount of the
    Bonds are payable from the income of a specific project or authority and
    are not supported by the issuer's power to levy taxes.  The portfolio is
    divided for purpose of issue as follows:  Coal Power 1, Electric and Gas
    1, Federally Insured Mortgage 2, Hospital 6, Insured Multi-Family Housing
    1, Natural Resource 1, Nuclear Power 3, Pollution Control 3, Sewer Systems
    1, University Facility 1, Utility 1, Waste Water 1 and Water 3.  For an
    explanation of the significance of these factors see "The Trust--
    Portfolio" in Part B of this Prospectus. 

          As of December 31, 1993, $3,915,000 (approximately 35.7% of the
    aggregate principal amount of the Bonds) were original issue discount
    bonds.  Of these original issue discount bonds, $3,915,000 (approximately
    35.7% of the aggregate principal amount of the Bonds) were Zero Coupon
    Bonds.  Zero Coupon Bonds do not provide for the payment of any current
    interest and provide for payment at maturity at par value unless sooner
    sold or redeemed.  The market value of Zero Coupon Bonds is subject to
    greater fluctuations than coupon bonds in response to changes in interest
    rates.  None of the aggregate principal amount of the Bonds in the Trust
    were purchased at a "market" discount from par value at maturity,
    approximately 64.3% were purchased at a premium and none were purchased at
    par.  For an explanation of the significance of these factors see
    "Discount and Zero Coupon Bonds" in Part B of this Prospectus. 

          None of the Bonds in the Trust are subject to the federal individual
    alternative minimum tax under the Tax Reform Act of 1986.  See "Tax
    Status" in Part B of this Prospectus. 

    
    
   
    <PAGE>
                       FINANCIAL AND STATISTICAL INFORMATION


    Selected data for each Unit outstanding for the periods listed below:
    
    
   
                                                                    Distribu-
                                                                    tions of
                                          Distributions of Interest Principal
                                          During the Period (per Unit)  During
                               Net Asset *            Semi-            the
                    Units Out-   Value    Monthly   Annual  Annual  Period
    Period Ended     standing  Per Unit   Option    Option  Option (Per Unit)

    December 31, 1991 11,000   $611.75    $46.80   $47.44   $47.62   -0- 
    December 31, 1992 11,000    603.16     46.80    47.40    47.59   -0- 
    December 31, 1993 11,000    550.65     46.14    46.74    46.93 $37.24


    *     Net Asset Value per Unit is calculated by dividing net assets as
          disclosed in the "Statement of Net Assets" by the number of Units
          outstanding as of the date of the Statement of Net Assets.  See
          Note 5 of Notes to Financial Statements for a description of the
          components of Net Assets.
        
    <PAGE>

Independent Auditors' Report


The Sponsor, Trustee and Certificateholders
Insured Municipal Securities Trust, 21st Discount Series:


We have audited the accompanying statement of net assets, including the
portfolio, of Insured Municipal Securities Trust, 21st Discount Series
as of December 31, 1993, and the related statements of operations, and
changes in net assets for each of the years in the three year period
then ended.  These financial statements are the responsibility of the
Trustee (see note 2).  Our responsibility is to express an opinion on
these financial statements based on our audits.

We conducted our audits in accordance with generally accepted auditing
standards.  Those standards require that we plan and perform the audit
to obtain reasonable assurance about whether the financial statements
are free of material misstatement.  An audit includes examining, on a
test basis, evidence supporting the amounts and disclosures in the
financial statements.  Our procedures included confirmation of
securities owned as of December 31, 1993, by correspondence with the
Trustee.  An audit also includes assessing the accounting principles
used and significant estimates made by management, as well as
evaluating the overall financial statement presentation.  We believe
that our audits provide a reasonable basis for our opinion.

In our opinion, the financial statements referred to above present
fairly, in all material respects, the financial position of Insured
Municipal Securities Trust, 21st Discount Series as of December 31,
1993, and the results of its operations and the changes in its net
assets for each of the years in the three year period then ended in
conformity with generally accepted accounting principles.




KPMG Peat Marwick


New York, New York
March 31, 1994

<PAGE>

                       Statement of Net Assets

                          December 31, 1993 

Investments in marketable securities,
   at market value (cost $5,985,116)            $    5,934,923

Excess of other assets over
   total liabilities                                  122,245
                                               ----------------

Net assets 11,000 units of fractional
   undivided interest outstanding,
    $550.65 per unit)                            $   6,057,168
                                               ================


See accompanying notes to financial statements.
<PAGE>

<TABLE>

                         Statements of Operations
<CAPTION>
                                                 Years ended December 31,
                                      ------------  ---- ---------  ---- --------------
                                          1993             1992               1991
                                      ------------       ---------       --------------
<S>                                <C>                   <C>             <C>
Investment income - interest       $      538,264         552,469              549,356
                                      ------------       ---------       --------------

Expenses:
   Trustee's fees                          10,804          10,559               10,026
   Evaluator's fees                         3,558           3,288                2,772
   Sponsor's advisory fee                   1,433           1,433                1,433
                                      ------------       ---------       --------------

           Total expenses                  15,795          15,280               14,231
                                      ------------       ---------       --------------

           Investment income, net         522,469         537,189              535,125
                                      ------------       ---------       --------------

Realized and unrealized gain (loss) 
on investments:
   Realized loss on bonds
      sold or called                      (53,134)           -                 -
   Unrealized appreciation 
      (depreciation) for the year        (126,984)       (114,131)             146,440
                                      ------------       ---------       --------------

           Net gain (loss) 
             on investments              (180,118)       (114,131)             146,440
                                      ------------       ---------       --------------

           Net increase in net
             assets resulting
             from operations       $      342,351         423,058              681,565
                                      ============       =========       ==============

See accompanying notes to financial statements.

</TABLE>

<PAGE>

<TABLE>
                          Statements of Changes in Net Assets
<CAPTION>
                                                       Years ended December 31,
                                               ----------- -- ----------- -- ------------
                                                  1993           1992            1991
                                               -----------    -----------    ------------
<S>                                         <C>               <C>            <C>
      Operations:
         Investment income, net             $     522,469        537,189         535,125
         Realized loss on
           bonds sold or called                   (53,134)         -              - 
         Unrealized appreciation
           (depreciation) for the year           (126,984)      (114,131)        146,440
                                               -----------    -----------    ------------

                   Net increase in net
                      assets resulting
                      from operations             342,351        423,058         681,565

      Distributions to Certificateholders:
         Investment income                        510,284        517,539         517,517
         Principal                                409,641          -              - 
                                               -----------    -----------    ------------

                   Total distributions            919,925        517,539         517,517

                   Total increase (decrease)     (577,574)       (94,481)        164,048

      Net assets at beginning of year           6,634,742      6,729,223       6,565,175
                                               -----------    -----------    ------------

      Net assets at end of year (including
         undistributed net investment 
         income of $198,183,  $212,873 and
         $193,223 respectively)             $   6,057,168      6,634,742       6,729,223
                                               ===========    ===========    ============

      See accompanying notes to financial statements. 
</TABLE>

<PAGE>

Notes to Financial Statements

December 31, 1993, 1992 and 1991

(1)    Organization

Insured Municipal Securities Trust, 21st Discount Series (Trust) was
organized on June 25, 1986 by Bear, Stearns & Co. Inc. (Sponsor)
under the laws of the State of New York by a Trust Indenture and
Agreement, and is registered under the Investment Company Act
of 1940.

(2)    Summary of Significant Accounting Policies

United States Trust Company of New York (Trustee) has custody of and
responsibility for the accounting records and financial statements of
the Trust and is responsible for establishing and maintaining a
system of internal control related thereto.

The Trustee is also responsible for all estimates of expenses and
accruals reflected in the Trust's financial statements.  The
accompanying financial statements have been adjusted to record the
unrealized appreciation (depreciation) of investments and to record
interest income and expenses on the accrual basis.

The discount on the zero-coupon bonds is accreted by the interest
method over the respective lives of the bonds.  The accretion of such
discount is included in interest income; however, it is not
distributed until realized in cash upon maturity or sale of the
respective bonds.

Investments are carried at market value which is determined by either
Standard & Poor's Corporation or Moody's Investors Service, Inc.
(Evaluator) as discussed in Footnotes to Portfolio.  The market value
of the investments is based upon the bid prices for the bonds at the
end of the year, except that the market value on the date of deposit
represents the cost to the Trust based on the offering prices for
investments at that date.  The difference between cost (including
accumulated accretion of original issue discount on zero-coupon bonds)
and market value is reflected as unrealized appreciation (depreciation)
of investments.  Securities transactions are recorded on the trade date.
Realized gains (losses) from securities transactions are determined on
the basis of average cost of the securities sold or redeemed.

(3)    Income Taxes

The Trust is not subject to Federal income taxes as provided for by
the Internal Revenue Code.

(4)    Trust Administration

The fees and expenses of the Trust are incurred and paid on the basis
set forth under "Trust Expenses and Charges" in Part B of this
Prospectus.

The Trust Indenture and Agreement provides for interest distributions
as often as monthly (depending upon the distribution plan elected by
the Certificateholders).

The Trust Indenture and Agreement further requires that principal
received from the disposition of bonds, other than those bonds sold
in connection with the redemption of units, be distributed to
Certificateholders.

See "Financial and Statistical Information" in Part A of this
Prospectus for the amounts of per unit distributions during the years
ended December 31, 1993, 1992, and 1991.

The Trust Indenture and Agreement also requires the Trust to redeem
units tendered.  No units have been redeemed since the inception of
the Trust.

(5)    Net Assets

At December 31, 1993, the net assets of the Trust represented the
interest of Certificateholders as follows:

Original cost to Certificateholders            $ 6,744,197
Less initial gross underwriting commission        (370,920)
                                                  6,373,277

Cost of securities sold or called                  (464,144)
Net unrealized depreciation                         (50,193)
Undistributed net investment income                 198,183
Undistributed proceeds from bonds
  sold or called                                         45

            Total                               $ 6,057,168


The original cost to Certificateholders, less the initial gross
underwriting commission, represents the aggregate initial public
offering price net of the applicable sales charge on 11,000 units
of fractional undivided interest of the Trust as of the date
of deposit.

Undistributed net investment income includes accumulated accretion
of original issue discount of $75,983.


See accompanying footnotes to portfolio and notes to financial statements.
<PAGE>

<TABLE>

INSURED MUNICIPAL SECURITIES TRUST, 21ST DISCOUNT SERIES

Portfolio 
December 31, 1993
<CAPTION>

Port-   Aggregate                                  Coupon Rate/   Redemption Feature
folio   Principal       Name of Issuer    Ratings  Date(s) of     S.F.--Sinking Fund          Market
No.     Amount       and Title of Bonds    (1)    Maturity(2)    Ref.-Refunding (2)(7)      Value(3)
- --      ---------    --------------------   ----   ------------   ----------------------    ----------
<S>   <C>            <C>                    <C>    <C>            <C>                       <C>
 1    $   300,000    Department of          AAA    8.875%         No Sinking Fund           $  344,796
                     Natural Resources of          7/01/2004      7/01/96 @ 102 Ref.
                     Florida Save Our
                     Coast Revenue Bonds, 
                     1985 Series (MBIA)
                     (5)



 2         80,000    Jacksonville           AAA    8.750          6/01/01 @ 100 S.F.            87,722
                     (Florida) Health              6/01/2005      6/01/95 @ 102 Ref.
                     Facilities Authority 
                     Hospital Revenue
                     Refunding Bonds
                     (Baptist Medical
                     Center Project) 1985 
                     Series  (MBIA) (5)


 3         55,000    City of Orlando,       AAA    8.875          10/01/01 @ 100 S.F.           61,287
                     Florida Waste Water           10/01/2014     10/01/95 @ 102 Ref.
                     System Revenue
                     Bonds, 1985 Series A 
                     (AMBAC) (5)


 4         50,000    City of Punta Gorda,   AAA    10.500         7/01/03 @ 100 S.F.            55,614
                     Florida Refunding             1/01/2014      1/01/95 @ 102 Ref.
                     and Improvement
                     Utility Revenue
                     Bonds, 1984 Series
                     (AMBAC) (5)


 5         50,000    West Coast Regional    AAA    9.250          4/01/07 @ 100 S.F.            56,124
                     Water Supply                  10/01/2013     10/01/95 @ 102 Ref.
                     Authority, Florida
                     Refunding Revenue
                     Bonds Hillsboro
                     Company Project
                     1985 Series (AMBAC)
                     (5)

 6        250,000    Development            AAA    11.625         No Sinking Fund              268,750
                     Authority of Burke            9/01/2014      9/01/94 @ 102 Ref.
                     County (Georgia)
                     Pollution Control
                     Revenue Bonds,
                     (Georgia Power
                     Company Plant Vogtle 
                     Project) 1984 Series 
                     2 (Financial
                     Guaranty)

 7        300,000    Development            AAA    10.125         No Sinking Fund              332,763
                     Authority of Burke            6/01/2015      6/01/95 @ 102 Ref.
                     County (Georgia)
                     Pollution Control
                     Revenue Bonds
                     (Georgia Power
                     Company Plant Vogtle 
                     Project) 1985
                     Series1 (Financial
                     Guaranty)



 8         85,000    Department of Budget   AAA    9.250%         7/01/04 @ 100 S.F.            94,200
                     and Finance of the            7/01/2012      7/01/95 @ 102 Ref.
                     State of Hawaii
                     Special Purpose
                     Revenue Bonds, (The
                     Queen's Medical
                     Center
                     Project)Refunding
                     1985 Series A
                     (Financial Guaranty) 
                     (5)

 9        250,000    City of Berwyn (Cook   AAA    9.200          12/01/05 @ 100 S.F.          280,395
                     County, Illinois)             12/01/2010     12/01/95 @ 102 Ref.
                     Corporate Purpose
                     Bonds, 1985 Series A 
                     (BIG)

 10       200,000    Chicago (Illinois)     AAA    10.500         6/01/05 @ 100 S.F.           212,730
                     School Finance                6/01/2009      6/01/94 @ 103 Ref.
                     Authority General
                     Obligation School
                     Assistance Bonds,
                     1984 Series E (1984) 
                     (MBIA) (5) 


11         85,000    Village of             AAA    9.500          1/01/06 @ 100 S.F.           107,526
                     Palantine, Illinois           1/01/2011      1/01/00 @ 102 Ref.
                     Corporate Purpose
                     Bonds, 1985 Series
                     Unlimited Tax (MBIA) 

12        100,000    Northwest Suburban     AAA    9.625          5/01/02 @ 100 S.F.           110,341
                     Municipal Joint               5/01/2005      5/01/95 @ 102 Ref.
                     Action Water Agency
                     (Cook, DuPage and
                     Kane Counties,
                     Illinois) Water
                     Supply System
                     Revenue Bonds, 1985
                     Series   (MBIA) (5)

13        150,000    City of Rosemont,      AAA    8.800          No Sinking Fund              167,173
                     Illinois Tax                  1/01/2002      1/01/96 @ 102 Ref.
                     Increment Bonds,
                     Project #2,  1985
                     Series C (BIG)

14        200,000    City of Rockport,      AAA    9.250          No Sinking Fund              221,160
                     Indiana Pollution             8/01/2014      8/01/95 @ 102 Ref.
                     Control Revenue
                     Bonds, (Indiana and
                     Michigan Electric
                     Company Project)
                     1985 Series A (BIG)

15        300,000    City of Rockport,      AAA    9.375          No Sinking Fund              333,621
                     Indiana Pollution             9/01/2014      9/01/95 @ 102 Ref.
                     Control Revenue
                     Bonds, 1985 Series A 
                     for AEP Generating
                     Company (Financial
                     Guaranty)

16        520,000    Michigan State         AAA    8.875          1/01/04 @ 100 S.F.           557,669
                     Housing Development           7/01/2017      7/01/95 @ 103 Ref.
                     Authority
                     Multi-Family Insured 
                     Housing Bonds 1985
                     Series A (Financial
                     Guaranty)

17        500,000    County of Monroe,      AAA    9.625          12/01/96 @ 100 S.F.          569,925
                     Michigan Pollution            12/01/2015     12/01/95 @ 103 Ref.
                     Control Revenue
                     Bonds, (Detroit
                     Edison Company
                     Project) 1985 Series 
                     A (AMBAC)


18        160,000    Montana Board of       AAA    9.350%         No Sinking Fund              182,861
                     Regents Higher                11/15/2001     11/15/95 @ 103 Ref.
                     Education, Montana
                     State University
                     Facility Refunding
                     Revenue Bonds, 1985
                     Series A (MBIA) (5)

 19       500,000    Oklahoma City,         AAA    9.250          5/01/06 @ 100 S.F.           563,900
                     Oklahoma Municipal            5/01/2018      11/01/95 @ 102 Ref.
                     Improvement
                     Authority Water
                     System Revenue Bonds 
                     Refunding 1985
                     Series A (AMBAC) (5) 


20         75,000    Berks County,          AAA    9.625          6/15/05 @ 100 S.F.            82,897
                     Pennsylvania                  6/15/2015      6/15/95 @ 102 Ref.
                     Municipal Authority
                     Hospital Revenue
                     Bonds (Franciscan
                     Health System/Saint
                     Joseph Hospital,
                     Reading,
                     Pennsylvania)1985
                     Series (BIG)

21        100,000    Dauphin County         AAA    9.750          7/01/99 @ 100 S.F.           105,680
                     Hospital Authority            7/01/2004      7/01/94 @ 102 Ref.
                     (Pennsylvania)
                     Hospital Revenue
                     Refunding Bonds,
                     1984 Series
                     (Harrisburg
                     Hospital) (MBIA) (5) 

22        100,000    Dauphin County         AAA    9.875          7/01/99 @ 100 S.F.           105,742
                     Hospital Authority            7/01/2014      7/01/94 @ 102 Ref.
                     (Pennsylvania)
                     Hospital Revenue
                     Refunding Bonds,
                     1984 Series
                     (Harrisburg
                     Hospital) (MBIA) (5) 

23         60,000    Mount Lebanon,         AAA    9.125          1/01/96 @ 100 S.F.            67,735
                     Pennsylvania                  7/01/2006      1/01/96 @ 102 Ref.
                     Hospital Authority
                     Hospital Revenue
                     Refunding  1985
                     Series (St. Clair
                     Memorial Hospital)
                     (Financial Guaranty) 
                     (5)

24        100,000    Dallas County, Texas   AAA    8.750          5/15/06 @ 100 S.F.           107,428
                     Utility and                   5/15/2015      5/15/95 @ 100 Ref.
                     Reclamation District 
                     Unlimited Ad Valorem 
                     Tax Bonds, 1985
                     Series (MBIA) (5)

25a       330,000    City of Houston,       AAA    9.375          12/01/06 @ 100 S.F.          374,316
                     Texas Sewer System            12/01/2013     12/01/95 @ 102  Ref.
                     Junior Lien Revenue
                     Refunding Bonds,
                     1985 Series
                     (Financial Guaranty) 
                     (5)

25b        50,000    City of Houston,       AAA    9.375          12/01/06 @ 100 S.F.           56,715
                     Texas Sewer System            12/01/2013     12/01/95 @ 102  Ref.
                     Junior Lien Revenue
                     Refunding Bonds,
                     1985 Series
                     (Financial Guaranty) 
                     (5)

26         90,000    City of San Antonio,   AAA    9.375          2/01/05 @ 100 S.F.            97,251
                     Texas Electric and            2/01/2009      2/01/95 @ 101.5 Ref.
                     Gas System 
                     Improvement Bonds,
                     New 1985 Series A
                     (BIG) (5)

27        100,000    Intermountain Power    AAA    9.625%         7/01/06 @ 100 S.F.           111,845
                     Agency (a political           7/01/2008      7/01/95 @ 102.5 Ref.
                     subdivision of the
                     State of Utah) Power 
                     Supply Revenue
                     Refunding Bonds,
                     1985 Series A
                     (AMBAC) (5)

28        100,000    Franklin County,       AAA    9.625          9/01/00 @ 100 S.F.           109,316
                     Washington Public             9/01/2002      3/01/95 @ 102 Ref.
                     Utility District #1
                     1985 Series (AMBAC)
                     (5)

29        520,000    The District of        AAA    0.000          5/01/05 @ 11.975 S.F.         20,920
                     Columbia Multi-Unit           11/01/2025     11/01/98 @ 6.415 Ref. 
                     Housing Finance
                     Corporation Mortgage 
                     Revenue Bonds, 1983
                     Series  (FHA Insured 
                     Mortgage
                     Loan-Congress Park
                     II Apartments
                     Section 8 Assisted
                     Project) (MBIA)

30      3,195,000    District of Columbia   AAA    0.000          2/01/09 @ 13.943 S.F.         86,521
                     Housing Finance               2/01/2027      2/01/04 @ 8.067 Ref.
                     Agency Multi-Family
                     Mortgage Revenue
                     Bonds, 1984 Series                                                     _   _
        _       _    (FHA Insured
                     Mortgage
                     Loan-Benning Heights 
                     Project-100% Section 
                     8 Assisted) (MBIA)


        ---------                                                                           ----------
     $  8,955,000                                                                        $   5,934,923
        =========                                                                           ==========

        See accompanying footnotes to portfolio and notes to financial statements.
</TABLE>

<PAGE>

Footnotes to Portfolio

December 31, 1993


(1)  All ratings are by Standard & Poor's Corporation.  A brief
description of the ratings symbols and their meanings is set forth
under "Description of Bond Ratings" in Part B of this Prospectus.

(2)  See "The Trust - Portfolio" in Part B of this Prospectus for an
explanation of redemption features.  See "Tax Status" in Part B of
this Prospectus for a statement of the Federal tax consequences to a
Certificateholder upon the sale, redemption or maturity of a bond.

(3)  At December 31, 1993, the net unrealized depreciation of all
the bonds was comprised of the following:

    Gross unrealized appreciation                 $ 94,636 
    Gross unrealized depreciation                 (144,829)

    Net unrealized depreciation                 $  (50,193) 

(4)  The annual interest income, based upon bonds held at December 31,
1993, (excluding accretion of original issue discount on zero-coupon
bonds) to the Trust is $497,073.

(5) The bonds have been prerefunded and will be redeemed at the next
refunding call date.

(6) Bonds sold or called after December 31, 1993 are noted in a footnote
"Changes in Trust Portfolio" under "Description of Portfolio" in Part
A of this Prospectus.

(7)  The Bonds may also be subject to other calls, which may be permitted
or required by events which cannot be predicted (such as destruction,
condemnation, termination of a contract, or receipt of excess or
unanticipated revenues).
<PAGE>



              Note:  Part B of This Prospectus May Not Be Distributed
                     Unless Accompanied by Part A.                   

                         Please Read and Retain Both Parts
                     of This Prospectus For Future Reference.

                        INSURED MUNICIPAL SECURITIES TRUST

                                 Prospectus Part B
       
                              Dated:  April 29, 1994
        

                                     THE TRUST

    Organization

               "Insured Municipal Securities Trust" (the "Trust") consists of
    the "unit investment trust" designated as set forth in Part A.*  The
    Trust was created under the laws of the State of New York pursuant to a
    Trust Indenture and Agreement** (collectively, the "Trust Agreement"),
    dated the Date of Deposit, among Bear, Stearns & Co. Inc., as Sponsor,
    Kenny S&P Evaluation Services, as Evaluator, and, depending on the
    particular Trust, either The Bank of New York or United States Trust
    Company of New York, as Trustee.  The name of the Trustee for the Trust is
    contained in the "Summary of Essential Information" in Part A.  For a
    description of the Trustee for a particular Trust, see "Trust
    Administration--The Trustee."


    *     This Part B relates to the outstanding series of Insured Municipal
          Securities Trust or Insured Municipal Securities Discount Trust as
          reflected in Part A attached hereto.


    **    References in this Prospectus to the Trust Agreement are qualified
          in their entirety by the Trust Indenture and Agreement which is
          incorporated herein.


    <PAGE>

               On the Date of Deposit the Sponsor deposited with the Trustee
    long-term insured bonds, and/or delivery statements relating to contracts
    for the purchase of certain such bonds (the "Bonds") and cash or an
    irrevocable letter of credit issued by a major commercial bank in the
    amount required for such purchases.  Thereafter, the Trustee, in exchange
    for the Bonds so deposited delivered to the Sponsor the Certificates
    evidencing the ownership of all Units of the Trust.  The Trust consists of
    the Bonds described under "The Trust" in Part A, the interest (including,
    where applicable, earned original issue discount) on which, in the
    opinions of bond counsel to the respective issuers given at the time of
    original delivery of the Bonds, is exempt from regular federal income tax
    under existing law. 

               Each "Unit" outstanding on the Evaluation Date represented an
    undivided interest or pro rata share in the principal and interest of the
    Trust in the ratio of one Unit to the principal amount of Bonds in the
    Trust on such date as specified in Part A of this Prospectus.  To the
    extent that any Units are redeemed by the Trustee, the fractional
    undivided interest or pro rata share in the Trust represented by each
    unredeemed Unit will increase, although the actual interest in the Trust
    represented by such fraction will remain unchanged.  Units will remain
    outstanding until redeemed upon tender to the Trustee by Certificate-
    holders, which may include the Sponsor or the Underwriters, or until the
    termination of the Trust Agreement. 

    Objectives

       
               The Trust, one of a series of similar but separate unit
    investment trusts formed by the Sponsor, offers investors the opportunity
    to participate in a portfolio of long-term insured tax-exempt bonds with a
    greater diversification than they might be able to acquire themselves. 
    The objectives of the Trust are to preserve capital and to provide
    interest income (including, where applicable, earned original issue
    discount) which, in the opinions of bond counsel given at the time of
    original delivery of the Bonds, is exempt from regular federal income tax
    under existing law.  Such interest income may, however, be subject to the
    federal, individual and corporate alternative minimum taxes and to state
    and local taxes.  (See "Description of Portfolio" in Part A for a list of
    those Bonds which pay interest income subject to federal individual
    alternative minimum tax.  See also "Tax Status".)  Consistent with such
    objectives, the Sponsor has obtained bond insurance guaranteeing the
    scheduled payment of principal and interest on certain of the Bonds and
    has purchased, as to the remainder of each Trust Portfolio, Bonds which
    are already covered by insurance.  (See "Insurance on the Bonds".)  An
    investor will realize taxable income upon maturity or early redemption of
    the market discount bonds in a Trust portfolio and will realize, where
    applicable, tax-exempt income to the extent of the earned portion of
    interest, including original issue discount earned on the Bonds in a Trust
    portfolio.  Investors should be aware that there is no assurance the
    Trust's objectives will be achieved as these objectives are dependent on
    the continuing ability of the issuers of the Bonds to meet their interest
    and principal payment requirements, on the abilities of the Insurance
    Companies to meet their obligations under the policies of insurance issued
    on the Bonds, on the continuing satisfaction of the Bonds of the
    conditions required for the exemption of interest thereon from regular
    federal income tax and on the market value of the Bonds, which can be
    affected by fluctuations in interest rates and other factors. 
        
               Since disposition of Units prior to final liquidation of each
    Trust may result in an investor receiving less than the amount paid for
    such Units (see "Comparison of Public Offering Price, Sponsor's Repurchase
    Price and Redemption Price"), the purchase of a Unit should be looked upon
    as a long-term investment.  Neither the Trust nor the Total Reinvestment
    Plan are designed to be complete investment programs. 

    Portfolio

               All of the Bonds in the Trust were rated "AAA" by Standard &
    Poor's Corporation at the time originally deposited in the Trust.  (See
    "Insurance on the Bonds".)  The "AAA" rating was assigned to the Bonds by
    Standard & Poor's because each Bond was insured by a municipal bond
    guaranty insurance policy issued by a company whose claims-paying ability
    was rated "AAA" by Standard & Poor's at that time.  Due to a downgrading
    of the claims-paying ability of one of the insurers, as of the Evaluation
    Date, the Bonds in the Trusts which are insured by that company are no
    longer rated "AAA" by Standard & Poor's.  Therefore, the Units of those
    Trusts containing the downgraded bonds are no longer rated. 

               For information regarding (i) the number of issues in the
    Trust, (ii) the range of fixed maturities of the Bonds, (iii) the number
    of issues payable from the income of a specific project or authority and
    (iv) the number of issues constituting general obligations of a government
    entity, see "The Trust" and "Description of Portfolio" in Part A of this
    Prospectus. 

               When selecting Bonds for a Trust, the following factors, among
    others, were considered by the Sponsor:  (a) the quality of the Bonds and
    whether such Bonds, whether Sponsor-Insured or Pre-Insured, were rated
    "AAA" by Standard & Poor's Corporation, (b) the yield and price of the
    Bonds relative to other tax-exempt securities of comparable quality and
    maturity, (c) income to the Certificateholders of the Trust, (d) whether a
    bond was insured, or insurance was available for the Bonds at a reasonable
    cost, (e) in connection with Bonds for which bond insurance was obtained
    by the Sponsor, the quality of the Bonds and whether they were rated,
    without regard to such bond insurance, "A" or better by either Standard &
    Poor's Corporation or Moody's Investors Service, and (f) the
    diversification of the Trust portfolio, as to purpose of issue and
    location of issuer, taking into account the availability in the market of
    issues which meet the Trust's quality, rating, yield and price criteria. 
    Subsequent to the Date of Deposit, a Bond may cease to be rated or its
    rating may be reduced below that specified above.  Neither event requires
    an elimination of such Bond from a Trust but may be considered in the
    Sponsor's determination to direct the Trustee to dispose of the Bond.  See
    "Portfolio Supervision."  For an interpretation of the bond ratings see
    "Description of Bond Ratings."
       

               Housing Bonds.  Some of the aggregate principal amount of the
    Bonds may consist of obligations of state and local housing authorities
    whose revenues are primarily derived from mortgage loans to rental housing
    projects for low to moderate income families.  Since such obligations are
    usually not general obligations of a particular state or municipality and
    are generally payable primarily or solely from rents and other fees,
    adverse economic developments including failure or inability to increase
    rentals, fluctuations of interest rates and increasing construction and
    operating costs may reduce revenues available to pay existing obligations. 
    See "Description of Portfolio" in Part A for the amount of rental housing
    bonds contained therein.
        

               Hospital Revenue Bonds.  Some of the aggregate principal amount
    of the Bonds may consist of hospital revenue bonds.  Ratings of hospital
    bonds are often initially based on feasibility studies which contain
    projections of occupancy levels, revenues and expenses.  Actual experience
    may vary considerably from such projections.  A hospital's gross receipts
    and net income will be affected by future events and conditions including,
    among other things, demand for hospital services and the ability of the
    hospital to provide them, physicians' confidence in hospital management
    capability, economic developments in the service area, competition,
    actions by insurers and governmental agencies and the increased cost and
    possible unavailability of malpractice insurance.  Additionally, a major
    portion of hospital revenue typically is derived from federal or state
    programs such as Medicare and Medicaid which have been revised
    substantially in recent years and which are undergoing further review at
    the state and federal level.

       
               Proposals for significant changes in the health care system and
    the present programs for third party payment of health care costs are
    under consideration in Congress and many states.  Future legislation or
    changes in the areas noted above, among other things, would affect all
    hospitals to varying degrees and, accordingly, any adverse change in these
    areas may affect the ability of such issuers to make payment of principal
    and interest on such bonds.  See "Description of Portfolio" in Part A for
    the amount of hospital revenue bonds contained therein.
        

               Nuclear Power Facility Bonds.  Certain Bonds may have been
    issued in connection with the financing of nuclear generating facilities. 
    In view of recent developments in connection with such facilities,
    legislative and administrative actions have been taken and proposed
    relating to the development and operation of nuclear generating
    facilities.  The Sponsor is  unable to predict whether any such actions or
    whether any such proposals or litigation, if enacted or instituted, will
    have an adverse impact on the revenues available to pay the debt service
    on the Bonds in the portfolio issued to finance such nuclear projects. 
    See "Description of Portfolio" in Part A for the amount of bonds issued to
    finance nuclear generating facilities contained therein.

               Mortgage Subsidy Bonds.  Certain Bonds may be "mortgage subsidy
    bonds" which are obligations of which all or a significant portion of the
    proceeds are to be used directly or indirectly for mortgages on owner-
    occupied residences.  Section 103A of the Internal Revenue Code of 1954,
    as amended, provided as a general rule that interest on "mortgage subsidy
    bonds" will not be exempt from Federal income tax.  An exception is
    provided for certain "qualified mortgage bonds."  Qualified mortgage bonds
    are bonds that are used to finance owner-occupied residences and that meet
    numerous statutory requirements.  These requirements include certain
    residency, ownership, purchase price and target area requirements, ceiling
    amounts for state and local issuers, arbitrage restrictions and (for bonds
    issued after December 31, 1984) certain information reporting,
    certification, public hearing and policy statement requirements.  In the
    opinions of bond counsel to the issuing governmental authorities, interest
    on all the Bonds in a Trust that might be deemed "mortgage subsidy bonds"
    will be exempt from Federal income tax when issued.  See "Description of
    Portfolio" in Part A for the amount of mortgage subsidy Bonds contained
    therein. 

       
               Mortgage Revenue Bonds.  Certain Bonds may be "mortgage revenue
    bonds."  Under the Internal Revenue Code of 1986, as amended (the "Code")
    (and under similar provisions of the prior tax law) "mortgage revenue
    bonds" are obligations the proceeds of which are used to finance owner-
    occupied residences under programs which meet numerous statutory
    requirements relating to residency, ownership, purchase price and target
    area requirements, ceiling amounts for state and local issuers, arbitrage
    restrictions, and certain information reporting certification, and public
    hearing requirements.  There can be no assurance that additional federal
    legislation will not be introduced or that existing legislation will not
    be further amended, revised, or enacted after delivery of these Bonds or
    that certain required future actions will be taken by the issuing
    governmental authorities, which action or failure to act could cause
    interest on the Bonds to be subject to federal income tax.  If any portion
    of the Bonds proceeds are not committed for the purpose of the issue,
    Bonds in such amount could be subject to earlier mandatory redemption at
    par, including issues of Zero Coupon Bonds (see "Discount and Zero Coupon
    Bonds").  See "Description of Portfolio" in Part A for the amount of
    mortgage revenue bonds contained therein. 

               Private Activity Bonds.  The portfolio of the Trust may contain
    other Bonds which are "private activity bonds" (often called Industrial
    Revenue Bonds ("IRBs") if issued prior to 1987) which would be primarily
    of two types:  (1) Bonds for a publicly owned facility which a private
    entity may have a right to use or manage to some degree, such as an
    airport, seaport facility or water system and (2) facilities deemed owned
    or beneficially owned by a private entity but which were financed with
    tax-exempt bonds of a public issuer, such as a manufacturing facility or a
    pollution control facility.  In the case of the first type, bonds are
    generally payable from a designated source of revenues derived from the
    facility and may further receive the benefit of the legal or moral
    obligation of one or more political subdivisions or taxing jurisdictions. 
    In most cases of project financing of the first type, receipts or revenues
    of the Issuer are derived from the project or the operator or from the
    unexpended proceeds of the bonds.  Such revenues include user fees,
    service charges, rental and lease payments, and mortgage and other loan
    payments.
        

               The second type of issue will generally finance projects which
    are owned by or for the benefit of, and are operated by, corporate
    entities.  Ordinarily, such private activity bonds are not general
    obligations of governmental entities and are not backed by the taxing
    power of such entities, and are solely dependent upon the creditworthiness
    of the corporate user of the project or corporate guarantor.

               The private activity bonds in the Trust have generally been
    issued under bond resolutions, agreements or trust indentures pursuant to
    which the revenues and receipts payable under the issuer's arrangements
    with the users or the corporate operator of a particular project have been
    assigned and pledged to the holders of the private activity bonds.  In
    certain cases a mortgage on the underlying project has been assigned to
    the holders of the private activity bonds or a trustee as additional
    security.  In addition, private activity bonds are frequently directly
    guaranteed by the corporate operator of the project or by another
    affiliated company.  See "Description of Portfolio" in Part A for the
    amount of private activity bonds contained therein.

               Litigation.  Litigation challenging the validity under state
    constitutions of present systems of financing public education has been
    initiated in a number of states.  Decisions in some states have been
    reached holding such school financing in violation of state constitutions. 
    In addition, legislation to effect changes in public school financing has
    been introduced in a number of states.  The Sponsor is unable to predict
    the outcome of the pending litigation and legislation in this area and
    what effect, if any, resulting changes in the sources of funds, including
    proceeds from property taxes applied to the support of public schools, may
    have on the school bonds in a Trust. 

               To the Sponsor's knowledge, there is no litigation pending as
    of the Date of Deposit with respect to any Bonds which might reasonably be
    expected to have a material adverse effect on a Trust.  Subsequent to the
    Date of Deposit, litigation may be initiated on a variety of grounds with
    respect to Bonds in a Trust.  Such litigation, as, for example, suits
    challenging the issuance of pollution control revenue bonds under
    recently-enacted environmental protection statutes, may affect the
    validity of such Bonds or the tax-free nature of the interest thereon. 
    The Sponsor is unable to predict whether any such litigation may be
    instituted or, if instituted, whether it might have a material adverse
    effect on a Trust. 

       
               Other Factors.  The Bonds in the Trust, despite their optional
    redemption provisions which generally do not take effect until 10 years
    after the original issuance dates of such bonds (often referred to as "ten
    year call protection"), do contain provisions which require the issuer to
    redeem such obligations at par from unused proceeds of the issue within a
    stated period.  In recent periods of declining interest rates there have
    been increased redemptions of bonds, particularly housing bonds, pursuant
    to such redemption provisions.  In addition, the Bonds in the Trusts are
    also subject to mandatory redemption in whole or in part at par at any
    time that voluntary or involuntary prepayments of principal on the
    underlying collateral are made to the trustee for such bonds or that the
    collateral is sold by the bond issuer.  Prepayments of principal tend to
    be greater in periods of declining interest rates; it is possible that
    such prepayments could be sufficient to cause a bond to be redeemed
    substantially prior to its stated maturity date, earliest call date or
    sinking fund redemption date.  

               The Bonds may also be subject to other calls, which may be
    permitted or required by events which cannot be predicted (such as
    destruction, condemnation, or termination of a contract).

               In 1976 the federal bankruptcy laws were amended so that an
    authorized municipal debtor could more easily seek federal court
    protection to assist in reorganizing its debts so long as certain
    requirements were met.  Historically, very few financially troubled
    municipalities have sought court assistance for reorganizing their debts;
    notwithstanding, the Sponsors are unable to predict to what extent
    financially troubled municipalities may seek court assistance in
    reorganizing their debts in the future and, therefore, what effect, if
    any, the applicable federal bankruptcy law provisions will have on the
    Trusts.
        

               The Trust may also include "moral obligation" bonds.  Under
    statutes applicable to such bonds, if any issuer is unable to meet its
    obligations, the repayment of such bonds becomes a moral commitment but
    not a legal obligation of the state or municipality in question.  See
    "Portfolio" and "Information Regarding the Trust" in Part A of this
    Prospectus for the amount of moral obligation bonds contained in each
    Trust. 

               Certain of the Bonds in the Trust are subject to redemption
    prior to their stated maturity dates pursuant to sinking fund or call
    provisions.  A sinking fund is a reserve fund appropriated specifically
    toward the retirement of a debt.  A callable bond is one which is subject
    to redemption or refunding prior to maturity at the option of the issuer. 
    A refunding is a method by which a bond is redeemed at or before maturity
    from the proceeds of a new issue of bonds.  In general, call provisions
    are more likely to be exercised when the offering side evaluation of a
    bond is at a premium over par than when it is at a discount from par.  A
    listing of the sinking fund and call provisions, if any, with respect to
    each of the Bonds is contained under "Portfolio".  Certificateholders will
    realize a gain or loss on the early redemption of such Bonds, depending
    upon whether the price of such Bonds is at a discount from or at a premium
    over par at the time Certificateholders purchase their Units. 

               Neither the Sponsor nor the Trustee shall be liable in any way
    for any default, failure or defect in any of the Bonds.  Because certain
    of the Bonds from time to time may be redeemed or will mature in
    accordance with their terms or may be sold under certain circumstances, no
    assurance can be given that a Trust will retain its present size and
    composition for any length of time.  The proceeds from the sale of a Bond
    or the exercise of any redemption or call provision will be distributed to
    Certificateholders on the next distribution date, except to the extent
    such proceeds are applied to meet redemptions of Units.  See "Trustee
    Redemption."

    Discount And Zero Coupon Bonds

               Some of the Bonds in a Trust may be original issue discount
    bonds.  The original issue discount, which is the difference between the
    initial purchase price of the Bonds and the face value, is deemed to
    accrue on a daily basis and the accrued portion will be treated as tax-
    exempt interest income for regular federal income tax purposes.  Upon sale
    or redemption, any gain realized that is in excess of the earned portion
    of original issue discount will be taxable as capital gain.  (See "Tax
    Status".)  The current value of an original issue discount bond reflects
    the present value of its face amount at maturity.  The market value tends
    to increase more slowly in early years and in greater increments as the
    Bonds approach maturity.  Of these original issue discount bonds, some of
    the aggregate principal amount of the Bonds in the Trust may be Zero
    Coupon Bonds.  (See "Description of Portfolios" in Part A.)  Zero Coupon
    Bonds do not provide for the payment of any current interest and provide
    for payment at maturity at face value unless sooner sold or redeemed.  The
    market value of Zero Coupon Bonds is subject to greater fluctuations than
    coupon bonds in response to changes in interest rates.  Zero Coupon Bonds
    generally are subject to redemption at compound accreted value based on
    par value at maturity.  Because the issuer is not obligated to make
    current interest payments, Zero Coupon Bonds may be less likely to be
    redeemed than coupon bonds issued at a similar interest rate, although
    certain zero coupon housing bonds may be subject to mandatory call
    provisions. 

       
               Some of the Bonds in the Trust may have been purchased at a
    "market" discount from par value at maturity.  This is because the coupon
    interest rates on the discount bonds at the time they were purchased and
    deposited in each Trust were lower than the current market interest rates
    for newly issued bonds of comparable rating and type.  At the time of
    issuance the discount bonds were for the most part issued at then current
    coupon interest rates.  The current returns (coupon interest income as a
    percentage of market price) of discount bonds will be lower than the
    current returns of comparably rated bonds of similar type newly issued at
    current interest rates because discount bonds tend to increase in market
    value as they approach maturity and the full principal amount becomes
    payable.  Gain on the disposition of a Bond purchased at a market discount
    generally will be treated as ordinary income, rather than capital gain, to
    the extent of accrued market discount.  A discount bond held to maturity
    will have a larger portion of its total return in the form of capital gain
    and less in the form of tax-exempt interest income than a comparable bond
    newly issued at current return, and a lower current market value than
    otherwise comparable bonds with a shorter term of maturity.  If interest
    rates rise, the value of discount bonds will decrease; and if interest
    rates decline, the value of discount bonds will increase.  The discount
    does not necessarily indicate a lack of market confidence in the issuer. 
        

    Insurance On The Bonds

               Each Bond in the Trust is insured by a municipal bond guaranty
    insurance policy, or in the case of Firemen's by a financial guaranty
    insurance policy, covering scheduled payment of principal and interest on
    such Bond.  See "Insurance" in Part A.  This insurance has been obtained
    either by the issuer of the Bond ("Pre-Insured Bonds"), or by the Sponsor
    ("Sponsor-Insured Bonds") with respect to Bonds which were not insured
    prior to their deposit in the Trusts.  The insurance policies on the Bonds
    are non-cancelable and will continue in force so long as the Bonds are
    outstanding and the insurers remain in business.  The insurance policies
    guarantee the timely payment of principal and interest on the Bonds but do
    not guarantee the market value of the Bonds or the value of the Units.  No
    representation is made herein as to any Bond insurer's ability to meet its
    obligations under a policy of insurance relating to any of the Bonds.  An
    insurance company that is required to pay interest and/or principal in
    respect of any Bond will succeed and be subrogated to the Trustee's right
    to collect such interest and/or principal from the issuer and to other
    related rights of the Trustee with respect to any such Bond.

               Sponsor-Insured Bonds.  For those Bonds which are not covered
    by an insurance policy obtained by the issuers of such Bonds, the Sponsor
    has obtained bond insurance from either Bond Investors Guaranty ("BIG"),
    Financial Guaranty Insurance Company ("Financial Guaranty"), Municipal
    Bond Insurance Association ("MBIA") or Municipal Bond Investors Assurance
    Corporation ("MBIA Corp.") in an effort to protect Certificateholders
    against nonpayment of principal and interest in respect of such Bonds (the
    "Sponsor-Insured Bonds").  The bond insurance on the Sponsor-Insured Bonds
    covers the Sponsor-Insured Bonds deposited in a Trust at the time that
    they are physically delivered to the Trustee (in the case of bearer bonds)
    or registered in the name of the Trustee or its nominee or delivered along
    with an assignment (in the case of registered bonds) or registered in the
    name of the Trustee or its nominee (in the case of bonds held in book-
    entry form).  Accordingly, although contracts to purchase Sponsor-Insured
    Bonds are not covered by the bond insurance obtained by the Sponsor, such
    Bonds will be insured when they are deposited in the Trust.  When
    selecting Bonds for a Trust prior to obtaining insurance thereon, the
    Sponsor considers the factors listed under "Portfolio", among others.  The
    insurers of the Sponsor-Insured Bonds apply their own standards in
    determining whether to insure the Sponsor-Insured Bonds.  To the extent
    that the standards of such insurers are more restrictive than those of the
    Sponsor, the Sponsor's investment criteria have been limited to the more
    restrictive standards. 

       
               Pre-Insured Bonds.  The Bonds which are insured under policies
    obtained by the Bond issuers are insured by AMBAC Indemnity Corporation
    ("AMBAC"), BIG, Financial Guaranty, Financial Security Insurance, Inc.
    ("Financial Security"), Firemen's Insurance Company of Newark, New Jersey
    ("Firemen's"), Industrial Indemnity Company ("IIC") (which operates the
    Health Industry Board Insurance Program ("HIBI Program")), MBIA, MBIA
    Corp., or United States Fidelity and Guaranty Company ("USF&G")
    (collectively, the "Insurance Companies").  The cost of this insurance is
    borne by the respective issuers of the Pre-Insured Bonds.  The percentage
    of the Portfolio insured by each Insurance Company, if any, is set forth
    under "Insurance" in Part A. 

               AMBAC is a Wisconsin-domiciled stock insurance company,
    regulated by the Insurance Department of the State of Wisconsin, and
    licensed to do business in 50 states, the District of Columbia and the
    Commonwealth of Puerto Rico, with admitted assets (unaudited) of
    approximately $1,936,000,000 and statutory capital (unaudited) of
    approximately $1,096,000,000 as of September 30, 1993.  Statutory capital
    consists of the statutory contingency reserve and policyholders' surplus
    of the insurance company.  AMBAC is a wholly owned subsidiary of AMBAC,
    Inc., a 100% publicly-held company.  
        

               As of the Evaluation Date, the claims-paying ability of AMBAC
    has been rated "AAA" by Standard & Poor's. 

       
               Financial Guaranty, a New York stock insurance corporation, is
    a wholly-owned subsidiary of FGIC Corporation ("FGIC"), a Delaware holding
    company.  FGIC is a wholly-owned subsidiary of General Electric Capital
    Corporation ("GECC").  Neither FGIC nor GECC is obligated to pay the debts
    of or the claims against Financial Guaranty.  Financial Guaranty is
    domiciled in the State of New York and is subject to regulation by the
    State of New York Insurance Department.  As of December 31, 1993, the
    total capital and surplus of Financial Guaranty was approximately
    $777,000,000.  Financial Guaranty is currently authorized to write
    insurance in all 50 states and the District of Columbia.  
        

               As of the Evaluation Date, the claims-paying ability of
    Financial Guaranty has been rated "AAA" by Standard & Poor's. 

       
               Firemen's, which was incorporated in New Jersey in 1855, is a
    wholly-owned subsidiary of The Continental Corporation ("Continental") and
    a member of The Continental Insurance Companies, a group of property and
    casualty insurance companies.  It provides unconditional and non-
    cancelable insurance on industrial development revenue bonds.  As of
    September 30, 1993, the total net admitted assets (unaudited) of Firemen's
    were $2,226,579,000 and its statutory surplus (unaudited) was
    $495,752,845.

               As of the Evaluation Date, the claims-paying ability of
    Continental, Firemen's parent, has been rated "AA-" by Standard & Poor's. 
    As a result of this rating, the ratings of all Bonds insured by Firemen's,
    except pre-refunded bonds, are rated AA-.  Consequently, the Units of the
    Trusts containing Bonds insured by Firemen's are no longer rated.

               Financial Security is a monoline insurance company incorporated
    under the laws of the State of New York and is licensed, along with its
    two subsidiaries, to engage in the financial guaranty insurance business
    in 49 states, the District of Columbia and Puerto Rico.  Financial
    Security is an indirect wholly-owned subsidiary of Financial Security
    Assurance Holdings Ltd., which is in turn approximately 92.5% owned by
    U.S. WEST Capital Corporation ("U.S. WEST").  U.S. WEST is a subsidiary of
    U.S. WEST, Inc., which operates businesses involved in communications,
    data solutions, marketing services and capital assets. 
        
       
               Pursuant to an intercompany agreement, liabilities on financial
    guaranty insurance written by Financial Security or either of its two
    subsidiaries are reinsured among such companies on an agreed upon
    percentage substantially proportional to their respective capital surplus
    and reserves, subject to applicable statutory risk limitations.  In
    addition, Financial Security reinsures a portion of its liabilities under
    certain of its financial guaranty insurance policies with other reinsurers
    under various quota-share treaties and on a transaction-by-transaction
    basis.  Such reinsurance does not alter or limit Financial Security's
    obligations under any financial guaranty insurance policy.  As of
    September 30, 1993, total shareholder equity of Financial Security and its
    wholly-owned subsidiaries was (unaudited) $585,935,000 and total unearned
    premium reserves was (unaudited) $216,434,000.

               As of the Evaluation Date, Financial Security's claims-paying
    ability has been rated "AAA" by Standard & Poor's.

               IIC is a wholly-owned subsidiary of Industrial Indemnity
    Holdings, Inc.  Industrial Indemnity Holdings, Inc. is a wholly owned
    subsidiary of Talegen Holdings, Inc. (formerly Crum and Forster, Inc.) 
    The address of the Insurer is 255 California Street, San Francisco,
    California 94111.  The following table sets forth summary statutory
    financial information with respect to Industrial Indemnity Company for the
    nine months ending September 1993, and for the years 1991 and 1992.  For
    the fiscal years ending December 31, 1991 and December 31, 1992,
    Industrial Indemnity Company participated in a Reinsurance Participation
    Agreement with certain other Crum and Forster, Inc. companies.  For 1991
    and 1992 the statutory financial information set forth is that of
    Industrial Indemnity Company only, as reported to the California
    Department of Insurance, and is not the combined financial information of
    the companies participating in the Reinsurance Participation Agreement. 
    As of January 1, 1993, Industrial Indemnity Company was not a participant
    in the Reinsurance Participation Agreement.  Additional information
    regarding the Industrial Indemnity Company can be obtained from the
    California Department of Insurance.
        
       
                      Nine Months Ended      Year Ended
                         September 30,       Year Ended      December 31, 
                              1993             1991               1991    

    Net Income (Loss)       102,986,582      <60,580,522>      27,489,374
    Total assets          1,996,780,555     1,732,927,506   1,602,412,749
    Total liabilities     1,748,037,431     1,517,825,778   1,379,857,700
    Policyholders' 
      surplus               248,743,124       215,101,728     222,555,049

               As of the Evaluation Date, the claims-paying ability of IIC has
    been rated "A" by Standard & Poor's.  As a result of this rating, the
    ratings of all Bonds in the Trusts insured by IIC, except pre-refunded
    bonds, are rated A.  Consequently, the Units of the Trusts containing
    Bonds insured by IIC are no longer rated. 
        

               Each insurance company comprising Municipal Bond Insurance
    Association ("MBIA", also known as the "Association") will be severally
    and not jointly obligated under the MBIA policy in the following
    respective percentages:  The Aetna Casualty and Surety Company, 33%;
    Fireman's Fund Insurance Company, 30%; The Travelers Indemnity Company,
    15%; Aetna Insurance Company*, 12%; and The Continental Insurance
    Company, 10%.  As a several obligor, each such insurance company will be
    obligated only to the extent of its percentage of any claim under the MBIA
    policy and will not be obligated to pay any unpaid obligation of any other
    member of MBIA.  Each insurance company's participation is backed by all
    of its assets.  However, each insurance company is a multiline insurer
    involved in several lines of insurance other than municipal bond
    insurance, and the assets of each insurance company also secure all of its
    other insurance policy and surety bond obligations.


    *     now known as Cigna Property and Casualty Company

    <PAGE>

               The following table sets forth certain financial information
    with respect to the five insurance companies comprising MBIA.  The
    statistics, which have been furnished by MBIA, are as reported by the
    insurance companies to the New York State Insurance Department and are
    determined in accordance with statutory accounting principals.  No
    representation is made herein as to the accuracy or adequacy of such
    information or as to the absence of material adverse changes in such
    information subsequent to the date thereof.  In addition, these numbers
    are subject to revision by the New York State Insurance Department which,
    if revised, could either increase or decrease the amounts.
       

                       MUNICIPAL BOND INSURANCE ASSOCIATION
                    FIVE MEMBER COMPANIES' ASSETS, LIABILITIES 
                            AND POLICYHOLDERS' SURPLUS
                                AS OF JUNE 30, 1993
                                  (000's omitted)


                                          New York   New York     New York
                                          Statutory  Statutory Policyholders'
                                          Assets    Liabilities  Surplus   

    The Aetna Casualty & Surety Company  $ 9,670,645  $ 8,278,113   $1,392,532
    Fireman's Fund Insurance Company       6,571,313    4,880,776    1,690,537
    The Travelers Indemnity Company       10,194,126    8,280,211    1,913,915
    Cigna Property and Casualty Company    6,198,088    5,634,331      563,757
      (Formerly Aetna Insurance Company)
    The Continental Insurance Company      2,574,504    2,223,194      351,310

       TOTAL                             $35,208,676  $29,296,625   $5,912,051



               Some of the members of the Association are among the
    shareholders of MBIA, Inc., a New York Stock Exchange listed company. 
    MBIA, Inc. is the parent of MBIA Corp.  MBIA Corp. commenced municipal
    bond insurance operations on January 5, 1987.  MBIA Corp. is a separate
    and distinct entity from the Association.  MBIA Corp. has no liability to
    the bondholders for the obligations of the Association under the Policy.
        
       
               MBIA Corp. is the principal operating subsidiary of MBIA Inc. 
    MBIA Inc. is not obligated to pay the debts of or claims against the
    Insurer.  MBIA Corp. is a limited liability corporation rather than a
    several liability association.  MBIA Corp. is domiciled, in the State of
    New York and licensed to do business in all 50 states, the District of
    Columbia and the Commonwealth of Puerto Rico.

               As of December 31, 1992 MBIA Corp. had admitted assets of $2.6
    billion (unaudited), total liabilities of $1.7 billion (audited), and
    total capital and surplus of $896 million (audited) determined in
    accordance with statutory accounting practices prescribed or permitted by
    insurance regulatory authorities.  As of December 31, 1993, MBIA Corp. had
    admitted assets of $3.1 billion (audited), total liabilities of $2.1
    billion (audited), and total capital and surplus of $978 million
    (unaudited) determined in accordance with statutory accounting practices
    prescribed or permitted by insurance regulatory authorities.  The address
    of MBIA Corp. is 113 King Street, Armonk, New York 10504.

               Effective December 31, 1989, MBIA Inc. acquired Bond Investors
    Group, Inc.  On January 5, 1990, MBIA acquired all of the outstanding
    stock of Bond Investors Group, Inc., the parent corporation of Bond
    Investors Guaranty Insurance Co. ("BIG").  Through a Reinsurance
    Agreement, BIG has ceded all of its net insured risks, as well as its
    unearned premium and contingency reserves, to MBIA and MBIA has reinsured
    BIG's net outstanding exposure.
        
       
               As of the Evaluation Date, the claims-paying ability of MBIA
    and MBIA Corp., have been rated "AAA" by Standard & Poor's. 

               Capital Guaranty is a monoline stock insurance company
    incorporated in Maryland, and is a wholly owned subsidiary of Capital
    Guaranty Corporation, a Maryland insurance holding company.  Capital
    Guaranty Corporation is a publicly owned company whose shares are traded
    on the New York Stock Exchange.  Other than their capital commitment to
    Capital Guaranty Corporation, the shareholders of Capital Guaranty
    Corporation are not obligated to pay the debts of, or the claims against,
    Capital Guaranty Insurance Company.  Capital Guaranty is authorized to
    provide insurance in 49 states, the District of Columbia and three U.S.
    territories.  As of December 31, 1993, the total statutory policyholders'
    surplus and contingency reserves of Capital Guaranty Insurance Company was
    approximately $190,986,527 (unaudited) and total admitted assets were
    approximately $284,503,855 (unaudited) as reported to the Insurance
    Department of the State of Maryland.
        

               As of the Evaluation Date, the claims-paying ability of
    Capital Guaranty has been rated "AAA" by Standard & Poor's. 

       
               As of the Date of Deposit, Standard & Poor's had rated the
    claims-paying ability of each of the above insurance companies "AAA" and
    had rated each of the Bonds in the Portfolio "AAA" because the insurance
    companies had insured the Bonds.  The assignment of such "AAA" ratings was
    due to Standard & Poor's assessment of the creditworthiness of the
    insurance companies and their ability to pay claims on their policies of
    insurance.  Subsequently, the rating of the claims-paying ability of the
    insurer of an underlying Bond may cease to be rated or may be downgraded
    which may result in a downgrading of the rating of the Units in the Trust. 
    For a discussion of the rating of the claims-paying ability of each of the
    Bond insurers see "Insurance On The Bonds".  For a list of Bond Ratings as
    of the Evaluation Date see the "Portfolio" in Part A of this Prospectus. 
    For a discussion of the rating assigned to the Units of the Trusts, see
    "the Trust" in Part A of this Prospectus.  The percentage of each Trust
    portfolio insured by each insurance company, if any, is set forth under
    "Insurance" in Part A. 
        
               The foregoing information relating to the above insurance
    companies is from published documents and other public sources and/or
    information provided by such insurance companies.  No representation is
    made herein as to the accuracy or adequacy of such information or as to
    the absence of material adverse changes in such information subsequent to
    the dates thereof, but the Sponsor is not aware that the information
    herein is inaccurate or incomplete. 


                                  PUBLIC OFFERING

    Offering Price

               The secondary market Public Offering Price per Unit is
    computed by adding to the aggregate bid price of the Bonds in the Trust
    divided by the number of Units outstanding, an amount based on the
    applicable sales charge times the aggregate offering price of the Bonds
    (see "Public Offering Price" in Part A for the applicable sales charge for
    the Trust).  A proportionate share of accrued interest on the Bonds to the
    expected date of settlement for the Units is added to the Public Offering
    Price.  Accrued interest is the accumulated and unpaid interest on a Bond
    from the last day on which interest was paid and is accounted for daily by
    the Trust at the initial daily rate set forth under "Summary of Essential
    Information" in Part A of this Prospectus.  This daily rate is net of
    estimated fees and expenses.  The Public Offering Price can vary on a
    daily basis from the amount stated in Part A in accordance with
    fluctuations in the prices of the Bonds and the price to be paid by each
    investor will be computed as of the date the Units are purchased.  The
    aggregate bid price evaluation of the Bonds is determined in the manner
    set forth under "Trustee Redemption."

               The Evaluator may obtain current bid or offering prices for
    the Bonds from investment dealers or brokers (including the Sponsor) that
    customarily deal in tax-exempt obligations or from any other reporting
    service or source of information which the Evaluator deems appropriate. 

    Accrued Interest

               An amount of accrued interest which represents accumulated
    unpaid or uncollected interest on a Bond from the last day on which
    interest was paid thereon will be added to the Public Offering Price and
    paid by the Certificateholder at the time Units are purchased.  Since the
    Trust normally receives the interest on Bonds twice a year and the
    interest on the Bonds in the Trust is accrued on a daily basis (net of
    estimated fees and expenses), the Trust will always have an amount of
    interest accrued but not actually received and distributed to Certificate-
    holders.  A Certificateholder will not recover his proportionate share of
    accrued interest until the Units are sold or redeemed, or the Trust is
    terminated.  At that time, the Certificateholder will receive his
    proportionate share of the accrued interest computed to the settlement
    date in the case of a sale or termination and to the date of tender in the
    case of redemption. 

    Employee Discounts

               Employees and their immediate families of Bear, Stearns & Co.
    Inc. and of any underwriter of a Trust, pursuant to employee benefit
    arrangements, may purchase Units of a Trust at a price equal to the
    offering side evaluation of the underlying securities in a Trust during
    the initial offering period and at the bid side thereafter, divided by the
    number of Units outstanding plus a reduced charge of $10.00 per Unit. 
    Such arrangements result in less selling effort and selling expenses than
    sales to employee groups of other companies.  Resales or transfers of
    Units purchased under the employee benefit arrangements may only be made
    through the Sponsor's secondary market, so long as it is being maintained.


    Distribution Of Units
       

               Certain banks and thrifts will make Units of the Trust
    available to their customers on an agency basis.  A portion of the sales
    charge paid by their customers is retained by or remitted to the banks. 
    Under the Glass-Steagall Act, banks are prohibited from underwriting
    Units; however, the Glass-Steagall Act does permit certain agency
    transactions and the banking regulators have indicated that these
    particular agency transactions are permitted under such Act.  In addition,
    state securities laws on this issue may differ from the interpretations of
    federal law expressed herein and banks and financial institutions may be
    required to register as dealers pursuant to state law.

               The Sponsor intends to qualify the Units for sale in
    substantially all States through the Underwriters and through dealers who
    are members of the National Association of Securities Dealers, Inc.  Units
    may be sold to dealers at prices which represent a concession of up to (a)
    4% of the Public Offering Price for the Insured Municipal Securities Trust
    Series or (b) $25.00 per unit for the Insured Municipal Securities Trust
    Discount Series, subject to the Sponsor's right to change the dealers'
    concession from time to time.  In addition, for transactions of 1,000,000
    Units or more, the Sponsor intends to negotiate the applicable sales
    charge and such charge will be disclosed to any such purchaser.  Such
    Units may then be distributed to the public by the dealers at the Public
    Offering Price then in effect.  The Sponsor reserves the right to reject,
    in whole or in part, any order for the purchase of Units.  The Sponsor
    reserves the right to change the discounts from time to time.
        

    Sponsor's Profits

               The Sponsor will receive a gross commission on all Units sold
    in the secondary market equal to the applicable sales charge on each
    transaction.  (See "Offering Price".)  In addition, in maintaining a
    market for the Units (see "Sponsor Repurchase") the Sponsor will realize
    profits or sustain losses in the amount of any difference between the
    price at which it buys Units and the price at which it resells such Units.


               Participants in the Total Reinvestment Plan can designate a
    broker as the recipient of a dealer concession (see "Total Reinvestment
    Plan"). 

    Comparison of Public Offering Price, Sponsor's
      Repurchase Price And Redemption Price

               The secondary market Public Offering Price of Units will be
    determined on the basis of the current bid prices of the Bonds in the
    Trust, plus the applicable sales charge.  The value at which Units may be
    resold in the Secondary Market or redeemed will be determined on the basis
    of the current bid prices of the Bonds without any sales charge.  On the
    Evaluation Date, the Public Offering Price and the Sponsor's initial
    Repurchase Price per Unit (each based on the bid side evaluation of the
    Bonds in the Trust) each exceeded the Redemption Price and the Sponsor's
    secondary market Repurchase Price per Unit (based upon the current bid
    side evaluation of the Bonds in the Trust) by the amounts shown under
    "Summary of Essential Information" in Part A of this Prospectus.  For this
    reason, among others (including fluctuations in the market prices of such
    Bonds and the fact that the Public Offering Price includes the applicable
    sales charge), the amount realized by a Certificateholder upon any
    redemption of Sponsor repurchase of Units may be less than the price paid
    for such Units. 


              ESTIMATED LONG TERM RETURN AND ESTIMATED CURRENT RETURN

       
               The rate of return on an investment in Units of each Trust is
    measured in terms of "Estimated Current Return" and "Estimated Long Term
    Return".
        

               Estimated Long Term Return is calculated by:  (1) computing
    the yield to maturity or to an earlier call date (whichever results in a
    lower yield) for each Bond in a Trust's portfolio in accordance with
    accepted bond practices, which practices take into account not only the
    interest payable on the Bond but also the amortization of premiums or
    accretion of discounts, if any; (2) calculating the average of the yields
    for the Bonds in each Trust's portfolio by weighing each Bond's yield by
    the market value of the Bond and by the amount of time remaining to the
    date to which the Bond is priced (thus creating an average yield for the
    portfolio of each Trust); and (3) reducing the average yield for the
    portfolio of each Trust in order to reflect estimated fees and expenses of
    that Trust and the maximum sales charge paid by Unitholders.  The
    resulting Estimated Long Term Return represents a measure of the return to
    Unitholders earned over the estimated life of each Trust.  The Estimated
    Long Term Return as of the day prior to the Evaluation Date is stated for
    the Trust under "Summary of Essential Information" in Part A.

               Estimated Current Return is computed by dividing the Estimated
    Net Annual Interest Income per Unit by the Public Offering Price per Unit. 
    In contrast to the Estimated Long Term Return, the Estimated Current
    Return does not take into account the amortization of premium or accretion
    of discount, if any, on the Bonds in the portfolios of each Trust. 
    Moreover, because interest rates on Bonds purchased at a premium are
    generally higher than current interest rates on newly issued bonds of a
    similar type with comparable rating, the Estimated Current Return per Unit
    may be affected adversely if such Bonds are redeemed prior to their
    maturity.  On the day prior to the Evaluation Date, the Estimated Net
    Annual Interest Income per Unit divided by the Public Offering Price
    resulted in the Estimated Current Return stated for each Trust under
    "Summary of Essential Information" in Part A.

               The Estimated Net Annual Interest Income per Unit of each
    Trust will vary with changes in the fees and expenses of the Trustee and
    the Evaluator applicable to each Trust and with the redemption, maturity,
    sale or other disposition of the Bonds in each Trust.  The Public Offering
    Price will vary with changes in the bid prices of the Bonds.  Therefore,
    there is no assurance that the present Estimated Current Return or
    Estimated Long Term Return will be realized in the future.

               A schedule of cash flow projections is available from the
    Sponsor upon request.


                           RIGHTS OF CERTIFICATEHOLDERS

    Certificates

               Ownership of Units of the Trust is evidenced by registered
    Certificates executed by the Trustee and the Sponsor.  Certificates may be
    issued in denominations of one or more Units and will bear appropriate
    notations on their faces indicating which plan of distribution has been
    selected by the Certificateholder.  Certificates are transferable by
    presentation and surrender to the Trustee properly endorsed and/or
    accompanied by a written instrument or instruments of transfer.  Although
    no such charge is presently made or contemplated, the Trustee may require
    a Certificateholder to pay $2.00 for each Certificate reissued or
    transferred and any governmental charge that may be imposed in connection
    with each such transfer or interchange.  Mutilated, destroyed, stolen or
    lost Certificates will be replaced upon delivery of satisfactory indemnity
    and payment of expenses incurred. 

    Interest And Principal Distributions

               Interest received by the Trust is credited by the Trustee to
    an Interest Account and a deduction is made to reimburse the Trustee
    without interest for any amounts previously advanced.  Proceeds
    representing principal received from the maturity, redemption, sale or
    other disposition of the Bonds are credited to a Principal Account. 

               Distributions to each Certificateholder from the Interest
    Account are computed as of the close of business on each Record Date for
    the following Payment Date and consist of an amount substantially equal to
    one-twelfth, one-half or all of such Certificateholder's pro rata share of
    the Estimated Net Annual Interest Income in the Interest Account,
    depending upon the applicable plan of distribution.  Distributions from
    the Principal Account (other than amounts representing failed contracts,
    as previously discussed) will be computed as of each semi-annual Record
    Date, and will be made to the Certificateholders on or shortly after the
    next semi-annual Payment Date.  Proceeds representing principal received
    from the disposition of any of the Bonds between a Record Date and a
    Payment Date which are not used for redemptions of Units will be held in
    the Principal Account and not distributed until the second succeeding
    semi-annual Payment Date.  No distributions will be made to Certificate-
    holders electing to participate in the Total Reinvestment Plan.  Persons
    who purchase Units between a Record Date and a Payment Date will receive
    their first distribution on the second Payment Date after such purchase. 

               Because interest payments are not received by the Trust at a
    constant rate throughout the year, interest distributions may be more or
    less than the amount credited to the Interest Account as of a given Record
    Date.  For the purpose of minimizing fluctuations in the distributions
    from the Interest Account, the Trustee will advance sufficient funds,
    without interest, as may be necessary to provide interest distributions of
    approximately equal amounts.  All funds in respect of the Bonds received
    and held by the Trustee prior to distribution to Certificateholders may be
    of benefit to the Trustee and do not bear interest to Certificateholders. 

               As of the first day of each month, the Trustee will deduct
    from the Interest Account, and, to the extent funds are not sufficient
    therein, from the Principal Account, amounts necessary to pay the expenses
    of the Trust (as determined on the basis set forth under "Trust Expenses
    and Charges").  The Trustee also may withdraw from said accounts such
    amounts, if any, as it deems necessary to establish a reserve for any
    applicable taxes or other governmental charges that may be payable out of
    the Trust.  Amounts so withdrawn shall not be considered a part of the
    Trust's assets until such time as the Trustee shall return all or any part
    of such amounts to the appropriate accounts.  In addition, the Trustee may
    withdraw from the Interest and Principal Accounts such amounts as may be
    necessary to cover purchases of Replacement Bonds and redemptions of Units
    by the Trustee. 

               The estimated monthly, semi-annual or annual interest
    distribution per Unit will initially be in the amount shown under Summary
    of Essential Information and will change and may be reduced as Bonds
    mature or are redeemed, exchanged or sold, or as expenses of the Trust
    fluctuate.  No distribution need be made from the Principal Account until
    the balance therein is an amount sufficient to distribute $1.00 per Unit. 

    Distribution Elections

               Interest is distributed monthly, semi-annually or annually,
    depending upon the distribution plan applicable to the Unit purchased. 
    Record Dates are the first day of each month for monthly distributions,
    the first day of each June and December for semi-annual distributions and
    the first day of each December for annual distributions.  Payment Dates
    will be the fifteenth day of each month following the respective Record
    Dates. 

               Certificateholders purchasing Units in the secondary market
    will initially receive distributions in accordance with the election of
    the prior owner.  Every October each Certificateholder may change his
    distribution election by notifying the Trustee in writing of such change
    between October 1 and November 1 of each year.  (Certificateholders
    deciding to change their election should contact the Trustee by calling
    the number listed on the back cover hereof for information regarding the
    procedures that must be followed in connection with this written
    notification of the change of election.)  Failure to notify the Trustee on
    or before November 1 of each year will result in a continuation of the
    plan for the following 12 months.

    Records

               The Trustee shall furnish Certificateholders in connection
    with each distribution a statement of the amount of interest, if any, and
    the amount of other receipts, if any, which are being distributed,
    expressed in each case as a dollar amount per Unit.  Within a reasonable
    time after the end of each calendar year the Trustee will furnish to each
    person who at any time during the calendar year was a Certificateholder of
    record, a statement showing (a) as to the Interest Account:  interest
    received (including amounts representing interest received upon any
    disposition of Bonds and earned original issue discount, if any), amounts
    paid for purchases of Replacement Bonds and redemptions of Units, if any,
    deductions for applicable taxes and fees and expenses of the Trust, and
    the balance remaining after such distributions and deductions, expressed
    both as a total dollar amount and as a dollar amount representing the pro
    rata share of each Unit outstanding on the last business day of such
    calendar year; (b) as to the Principal Account:  the dates of disposition
    of any Bonds and the net proceeds received therefrom (including any
    unearned original issue discount but excluding any portion representing
    accrued interest), deductions for payments of applicable taxes and fees
    and expenses of the Trust, amounts paid for purchases of Replacement Bonds
    and redemptions of Units, if any, and the balance remaining after such
    distributions and deductions, expressed both as a total dollar amount and
    as a dollar amount representing the pro rata share of each Unit
    outstanding on the last business day of such calendar year; (c) a list of
    the Bonds held and the number of Units outstanding on the last business
    day of such calendar year; (d) the Redemption Price per Unit based upon
    the last computation thereof made such calendar year; and (e) amounts
    actually distributed to Certificateholders during such calendar year from
    the Interest and Principal Accounts, separately stated, expressed both as
    total dollar amounts representing the pro rata share of each Unit
    outstanding on the last business day of such calendar year. 

               The Trustee shall keep available for inspection by Certifi-
    cateholders at all reasonable times during usual business hours, books of
    record and account of its transactions as Trustee, including records of
    the names and addresses of Certificateholders, Certificates issued or
    held, a current list of Bonds in the portfolio and a copy of the Trust
    Agreement. 


                                    TAX STATUS


               All Bonds acquired by the Trust were accompanied by copies of
    opinions of bond counsel to the issuing governmental authorities given at
    the time of original delivery of the Bonds to the effect that the interest
    thereon is exempt from regular federal income tax.  Such interest may,
    however, be subject to the federal corporate alternative minimum tax and
    to state and local taxes.  Neither the Sponsor nor the Trustee nor their
    respective counsel has made any review of the proceedings relating to the
    issuance of the Bonds or the bases for such opinion and express no opinion
    as to these matters, and neither the Trustee nor the Sponsor nor their
    respective counsel has made an independent examination or verification
    that the federal income tax status of the Bonds has not been altered since
    the time of the original delivery of those opinions. 

       
               The Revenue Reconciliation Act of 1993 ("P.L. 103-66") was
    recently enacted.  P.L. 103-66 increases maximum marginal income tax rates
    for individuals and corporations (generally effective for taxable years
    beginning after December 31, 1992), extends the authority to issue certain
    categories of tax-exempt bonds (qualified small issue bonds and qualified
    mortgage bonds), limits the availability of capital gain treatment for
    tax-exempt bonds purchased at a market discount, increases the amount of
    Social Security benefits subject to tax (effective for taxable years
    beginning after December 31, 1993) and makes a variety of other changes. 
    Prospective investors are urged to consult their own tax advisors as to
    the effect of P.L. 103-66 on an investment in Units.
        

               In rendering the opinion set forth below, counsel has examined
    the Agreement, the final form of Prospectus dated the date hereof (the
    "Prospectus") and the documents referred to therein, among others, and has
    relied on the validity of said documents and the accuracy and completeness
    of the facts set forth therein. 

               In the opinion of Battle Fowler, counsel for the Sponsor,
    under existing law:

          The Trust is not an association taxable as a corporation for federal
    income tax purposes under the Internal Revenue Code of 1986 (the "Code"),
    and income received by the Trust that consists of interest excludable from
    federal gross income under the Code will be excludable from the federal
    gross income of the Certificateholders of the Trust. 

          Each Certificateholder will be considered the owner of a pro rata
    portion of the Trust under Section 676(a) of the Code.  Thus, each Cer-
    tificateholder will be considered to have received his pro rata share of
    Bond interest when it is received by the Trust, and the net income
    distributable to Certificateholders that is exempt from federal income tax
    when received by the Trust will constitute tax-exempt income when received
    by the Certificateholders. 

       
          Gain (other than any earned original issue discount) realized on a
    sale or redemption of the Bonds or on a sale of a Unit is, however,
    includable in gross income for federal income tax purposes, generally as
    capital gain, although gain on the disposition of a Bond or a Unit
    purchased at a market discount generally will be treated as ordinary
    income, rather than capital gain, to the extent of accrued market
    discount.  (It should be noted in this connection that such gain does not
    include any amounts received in respect of accrued interest.)  Such gain
    may be long or short-term depending on the facts and circumstances. 
    Capital losses are deductible to the extent of capital gains; in addition,
    up to $3,000 of capital losses of non-corporate Certificateholders may be
    deducted against ordinary income.  Capital assets acquired on or after
    January 1, 1988 must be held for more than one year to qualify for long-
    term capital gain treatment.

          Each Certificateholder will realize taxable gain or loss when the
    Trust disposes of a Bond (whether by sale, exchange, redemption or payment
    at maturity), as if the Certificateholder had directly disposed of his pro
    rata share of such Bond.  The gain or loss is measured by the difference
    between (i) the tax cost of such pro rata share and (ii) the amount
    received therefor.  For this purpose, a Certificateholder's per Unit tax
    cost for each Bond is determined by allocating the total tax cost of each
    Unit among all the Bonds held in the Trust (in accordance with the portion
    of the Trust comprised by each Bond).  In order to determine the amount of
    taxable gain or loss, the Certificateholder's amount received is similarly
    allocated at that time.  The Certificateholder may exclude from the amount
    received any amounts that represent accrued interest or the earned portion
    of any original issue discount but may not exclude amounts attributable to
    market discount.  Thus, when a Bond is disposed of by the Trust at a gain,
    taxable gain will equal the difference between (i) the amount received and
    (ii) the amount paid plus any original issue discount (limited, in the
    case of Bonds issued after June 8, 1980, to the portion earned from the
    date of acquisition to the date of disposition).  Gain on the disposition
    of a Bond purchased at a market discount generally will be treated as
    ordinary income, rather than capital gain, to the extent of accrued market
    discount.  No deduction is allowed for the amortization of bond premium on
    tax-exempt bonds such as the Bonds in computing regular federal income
    tax. 
        

          Discount generally accrues based on the principle of compounding of
    accrued interest, not on a straight-line or ratable method, with the
    result that the amount of earned original issue discount is less in the
    earlier years and more in the later years of a bond term.  The tax basis
    of a discount bond is increased by the amount of accrued, tax-exempt
    original issue discount thus determined.  This method of calculation will
    produce higher capital gains (or lower losses) to a Certificateholder, as
    compared to the results produced by the straight-line method of accounting
    for original issue discount, upon an early disposition of a Bond by the
    Trust or of a Unit by a Certificateholder.

       
          A Certificateholder may also realize taxable income or loss when a
    Unit is sold or redeemed.  The amount received is allocated among all the
    Bonds in the Trust in the same manner as when the Trust disposes of Bonds
    and the Certificateholder may exclude accrued interest and the earned
    portion of any original issue discount (but not amounts attributable to
    market discount).  The return of a Certificateholder's tax cost is
    otherwise a tax-free return of capital. 

          A portion of social security benefits is includable in gross income
    for taxpayers whose "modified adjusted gross income" combined with a
    portion of their benefits exceeds a base amount.  The base amount is
    $25,000 for an individual, $32,000 for a married couple filing a joint
    return and zero for married persons filing separate returns.  Interest on
    tax-exempt bonds is to be added to adjusted gross income for purposes of
    computing the amount of Social Security benefits that are includable in
    gross income and determining whether an individual's income exceeds the
    base amount above which a portion of the benefits would be subject to tax. 
    For taxable years beginning after December 31, 1993, the amount of Social
    Security benefits subject to tax will be increased.
        

          Corporate Certificateholders are required to include in federal
    corporate alternative minimum taxable income 75 percent of the amount by
    which the adjusted current earnings (which will include tax-exempt
    interest) of the corporation exceeds the alternative minimum taxable
    income (determined without this item).  Further, interest on the Bonds is
    includable in a 0.12% additional corporate minimum tax imposed by the
    Superfund Amendments and Reauthorization Act of 1986 for taxable years
    beginning before January 1, 1996.  In addition, in certain cases, Subchap-
    ter S corporations with accumulated earnings and profits from Subchapter C
    years will be subject to a minimum tax on excess "passive investment
    income" which includes tax-exempt interest.

          Any proceeds received pursuant to the terms of the insurance on the
    Bonds that represent maturing interest on defaulted obligations will be
    excludable from federal gross income if, and to the same extent that, such
    interest would have been so excludable if paid by the issuers of such
    defaulted obligations. 

          The Trust is not subject to the New York State Franchise Tax on
    Business Corporations or the New York City General Corporation Tax.  For a
    Certificateholder who is a New York resident, however, a pro rata portion
    of all or part of the income of the Trust will be treated as the income of
    the Certificateholder under the income tax laws of the State and City of
    New York.  Similar treatment may apply in other states. 

               The exemption of interest on municipal obligations for federal
    income tax purposes does not necessarily result in exemption under the
    income tax laws of any state or political subdivision.  In general,
    municipal bond interest exempt from federal income tax is taxable income
    to residents of the State or City of New York under the tax laws of those
    jurisdictions unless the bonds are issued by the State of New York or one
    of its political subdivisions or by the Commonwealth of Puerto Rico or one
    of its political subdivisions.  For corporations doing business in New
    York State, interest earned on state and municipal obligations that are
    exempt from federal income tax, including obligations of New York State,
    its political subdivisions and instrumentalities, must be included in
    calculating New York State and New York City entire net income for
    purposes of calculating New York State and New York City franchise
    (income) tax.  The laws of the several states and local taxing authorities
    vary with respect to the taxation of such obligations and each Certifi-
    cateholder is advised to consult his own tax advisor as to the tax
    consequences of his Certificates under state and local tax laws. 

               In the case of Bonds that are industrial revenue bonds
    ("IRBs") or certain types of private activity bonds, the opinions of bond
    counsel to the respective issuing authorities indicate that interest on
    such Bonds is exempt from regular federal income tax.  However, interest
    on such Bonds will not be exempt from regular federal income tax for any
    period during which such Bonds are held by a "substantial user" of the
    facilities financed by the proceeds of such Bonds or by a "related person"
    thereof within the meaning of the Code.  Therefore, interest on any such
    Bonds allocable to a Certificateholder who is such a "substantial user" or
    "related person" thereof will not be tax-exempt.  Furthermore, in the case
    of IRBs that qualify for the "small issue" exemption, the "small issue"
    exemption will not be available or will be lost if, at any time during the
    three-year period beginning on the later of the date the facilities are
    placed in service or the date of issue, all outstanding tax-exempt IRBs,
    together with a proportionate share of any present issue, of an owner or
    principal user (or related person) of the facilities exceeds $40,000,000. 
    In the case of IRBs issued under the $10,000,000 "small issue" exemption,
    interest on such IRBs will become taxable if the face amount of the IRBs
    plus certain capital expenditures exceeds $10,000,000.

               In addition, a Bond can lose its tax-exempt status as a result
    of other subsequent but unforeseeable events such as prohibited
    "arbitrage" activities by the issuer of the Bond or the failure of the
    Bond to continue to satisfy the conditions required for the exemption of
    interest thereon from regular federal income tax.  No investigation has
    been made as to the current or future owners or users of the facilities
    financed by the Bonds, the amount of such persons' outstanding tax-exempt
    IRBs, or the facilities themselves, and no assurance can be given that
    future events will not affect the tax-exempt status of the Bonds. 
    Investors should consult their tax advisors for advice with respect to the
    effect of these provisions on their particular tax situation.

               Interest on indebtedness incurred or continued to purchase or
    carry the Units is not deductible for regular federal income tax purposes. 
    However, such interest is deductible for New York State and New York City
    income tax purposes by corporations that are required to include interest
    on the Bonds in New York State and New York City entire net income for
    purposes of calculating the New York State and New York City franchise
    (income) taxes.  In addition, under rules used by the Internal Revenue
    Service for determining when borrowed funds are considered used for the
    purpose of purchasing or carrying particular assets, the purchase of Units
    may be considered to have been made with borrowed funds even though the
    borrowed funds are not directly traceable to the purchase of Units.  Also,
    in the case of certain financial institutions that acquire Units, in
    general no deduction is allowed for interest expense allocable to the
    Units. 

               From time to time proposals have been introduced before
    Congress to restrict or eliminate the federal income tax exemption for
    interest on debt obligations similar to the Bonds in the Trust, and it can
    be expected that similar proposals may be introduced in the future.

               In a 1988 decision (South Carolina v. Baker), the U.S. Supreme
    Court held that the federal government may constitutionally require states
    to register bonds they issue and subject the interest on such bonds to
    federal income tax if not registered, and that there is no constitutional
    prohibition against the federal government's taxing the interest earned on
    state or other municipal bonds.  The Supreme Court decision affirms the
    authority of the federal government to regulate and control bonds such as
    the Bonds in the Trust and to tax interest on such bonds in the future. 
    The decision does not, however, affect the current exemption from taxation
    of the interest earned on the Bonds in the Trust in accordance with Sec-
    tion 103 of the Code. 

               The opinions of bond counsel or special tax counsel to the
    issuing governmental authorities to the effect that interest on the Bonds
    is exempt from regular federal income tax may be limited to law existing
    at the time the Bonds were issued, and may not apply to the extent that
    future changes in law, regulations or interpretations affect such Bonds. 
    Investors are advised to consult their own tax advisors for advice with
    respect to the effect of any legislative changes.


                                     LIQUIDITY

    Sponsor Repurchase

       
               The Sponsor, although not obligated to do so, intends to
    maintain a secondary market for the Units and continuously to offer to
    repurchase the Units.  The Sponsor's secondary market repurchase price,
    after the initial public offering is completed, will be based on the
    aggregate bid price of the Bonds in the Trust portfolio, determined by the
    Evaluator on a daily basis, and will be the same as the redemption price. 
    The aggregate bid price is determined by the Evaluator on a daily basis
    and completed on the basis set forth under "Trustee Redemption".  Certifi-
    cateholders who wish to dispose of their Units should inquire of the
    Sponsor as to current market prices prior to making a tender for
    redemption.  The Sponsor may discontinue repurchase of Units if the supply
    of Units exceeds demand, or for other business reasons.  The date of
    repurchase is deemed to be the date on which Certificates representing
    Units are physically received in proper form by Bear, Stearns & Co. Inc.,
    245 Park Avenue, New York, NY 10167.  Units received after 4 P.M., New
    York Time, will be deemed to have been repurchased on the next business
    day.  In the event a market is not maintained for the Units, a Certifi-
    cateholder may be able to dispose of Units only by tendering them to the
    Trustee for redemption. 
        

               Prospectuses relating to certain other bond trusts indicate an
    intention by the respective Sponsor, subject to change, to repurchase
    units on the basis of a price higher than the bid prices of the bonds in
    the trusts.  Consequently, depending on the prices actually paid, the
    secondary market repurchase price of other trusts may be computed on a
    somewhat more favorable basis than the repurchase price offered by the
    Sponsor for units of this Trust, although in all bond trusts, the purchase
    price of a unit depends primarily on the value of the bonds in the trust
    portfolio. 

               Units purchased by the Sponsor in the secondary market may be
    re-offered for sale by the Sponsor at a price based on the aggregate bid
    price of the Bonds in the Trust plus the applicable sales charge (see
    "Public Offering Price" in Part A) plus net accrued interest.  Any Units
    that are purchased by the Sponsor in the secondary market also may be
    redeemed by the Sponsor if it determines such redemption to be in its best
    interest. 

               The Sponsor may, under certain circumstances, as a service to
    Certificateholders, elect to purchase any Units tendered to the Trustee
    for redemption (see "Trustee Redemption").  Factors which the Sponsor will
    consider in making a determination will include the number of Units of all
    Trusts which it has in inventory, its estimate of the salability and the
    time required to sell such Units and general market conditions.  For
    example, if in order to meet redemptions of Units the Trustee must dispose
    of Bonds, and if such disposition cannot be made by the redemption date
    (seven calendar days after tender), the Sponsor may elect to purchase such
    Units.  Such purchase shall be made by payment to the Certificateholder
    not later than the close of business on the redemption date of an amount
    equal to the Redemption Price on the date of tender. 

    Trustee Redemption

               Units may also be tendered to the Trustee for redemption at
    its corporate trust office as set forth in Part A of this Prospectus, upon
    proper delivery of Certificates representing such Units and payment of any
    relevant tax.  At the present time there are no specific taxes related to
    the redemption of Units.  No redemption fee will be charged by the Sponsor
    or the Trustee.  Units redeemed by the Trustee will be cancelled. 

               Certificates representing Units to be redeemed must be
    delivered to the Trustee and must be properly endorsed or accompanied by
    proper instruments of transfer with signature guaranteed (or by providing
    satisfactory indemnity, as in the case of lost, stolen or mutilated
    Certificates).  Thus, redemptions of Units cannot be effected until
    Certificates representing such Units have been delivered by the person
    seeking redemption.  (See "Certificates".)  Certificateholders must sign
    exactly as their names appear on the faces of their Certificates.  In
    certain instances the Trustee may require additional documents such as,
    but not limited to, trust instruments, certificates of death, appointments
    as executor or administrator or certificates of corporate authority. 

               Within seven calendar days following a tender for redemption,
    or, if such seventh day is not a business day, on the first business day
    prior thereto, the Certificateholder will be entitled to receive in cash
    an amount for each Unit tendered equal to the Redemption Price per Unit
    computed as of the Evaluation Time set forth under "Summary of Essential
    Information" in Part A on the date of tender.  The "date of tender" is
    deemed to be the date on which Units are received by the Trustee, except
    that with respect to Units received after the close of trading on the New
    York Stock Exchange, the date of tender is the next day on which such
    Exchange is open for trading, and such Units will be deemed to have been
    tendered to the Trustee on such day for redemption at the Redemption Price
    computed on that day. 

               Accrued interest paid on redemption shall be withdrawn from
    the Interest Account, or, if the balance therein is insufficient, from the
    Principal Account.  All other amounts paid on redemption shall be
    withdrawn from the Principal Account.  The Trustee is empowered to sell
    Bonds in order to make funds available for redemptions.  Such sales, if
    required, could result in a sale of Bonds by the Trustee at a loss.  To
    the extent Bonds are sold, the size and diversity of the Trust will be
    reduced. 

               The Redemption Price per Unit is the pro rata share of each
    Unit in the Trust determined by the Trustee on the basis of (i) the cash
    on hand in the Trust or moneys in the process of being collected, (ii) the
    value of the Bonds in the Trust based on the bid prices of such Bonds and
    (iii) interest accrued thereon, less (a) amounts representing taxes or
    other governmental charges payable out of the Trust, (b) the accrued
    expenses of the Trust and (c) cash allocated for the distribution to Cer-
    tificateholders of record as of the business day prior to the evaluation
    being made.  The Evaluator may determine the value of the Bonds in the
    Trust (1) on the basis of current bid prices of the Bonds obtained from
    dealers or brokers who customarily deal in bonds comparable to those held
    by the Trust, (2) on the basis of bid prices for bonds comparable to any
    Bonds for which bid prices are not available, (3) by determining the value
    of the Bonds by appraisal, or (4) by any combination of the above.  The
    Evaluator will determine the aggregate current bid price evaluation of the
    Bonds in the Trust, taking into account the market value of the Bonds
    insured under the Bond Insurance Policy, in the manner described as set
    forth under "Public Offering--Offering Price".  Insurance does not
    guarantee the market value of the Bonds or the Units, and while Bond
    insurance represents an element of market value in regard to insured
    Bonds, its exact effect, if any, on market value cannot be predicted. 

               The Trustee is irrevocably authorized in its discretion, if
    the Sponsor does not elect to purchase a Unit tendered for redemption or
    if the Sponsor tenders a Unit for redemption, in lieu of redeeming such
    Unit, to sell such Unit in the over-the-counter market for the account of
    the tendering Certificateholder at prices which will return to the Cer-
    tificateholder an amount in cash, net after deducting brokerage
    commissions, transfer taxes and other charges, equal to or in excess of
    the Redemption Price for such Unit.  The Trustee will pay the net proceeds
    of any such sale to the Certificateholder on the day he would otherwise be
    entitled to receive payment of the Redemption Price. 

               The Trustee reserves the right to suspend the right of
    redemption and to postpone the date of payment of the Redemption Price per
    Unit for any period during which the New York Stock Exchange is closed,
    other than customary weekend and holiday closings, or trading on that
    Exchange is restricted or during which (as determined by the Securities
    and Exchange Commission) an emergency exists as a result of which disposal
    or evaluation of the Bonds is not reasonably practicable, or for such
    other periods as the Securities and Exchange Commission may by order
    permit.  The Trustee and the Sponsor is not liable to any person or in any
    way for any loss or damage which may result from any such suspension or
    postponement. 

               A Certificateholder who wishes to dispose of his Units should
    inquire of his bank or broker in order to determine if there is a current
    secondary market price in excess of the Redemption Price. 


                              TOTAL REINVESTMENT PLAN


               Under the Total Reinvestment Plan (the "Plan"), semi-annual
    and annual Certificateholders (except Texas residents*) may elect to have
    all interest and principal distributions, if any, with respect to their
    Units reinvested either in units of various series of "Insured Municipal
    Securities Trust" or "Municipal Securities Trust" which will have been
    created shortly before each semi-annual or annual Payment Date (a "Primary
    Series") or, if units of a Primary Series are not available, in units of a
    previously formed series of the Trust which have been repurchased by the
    Sponsor in the secondary market or which constitute a portion of the Units
    of the Trust not sold by the Sponsor prior to such Payment Date (a
    "Secondary Series") (Primary Series and Secondary Series are hereafter
    collectively referred to as "Available Series").  Series of "Municipal
    Securities Trustee" do not have insurance.  The first interest
    distribution to Certificateholders cannot be reinvested unless such
    distribution is scheduled for June 15 or December 15 in the case of semi-
    annual Certificateholders or December 15 in the case of annual Certifi-
    cateholders (each such date being referred to herein as the "Plan
    Reinvestment Date"). 


    *     Texas residents may elect to participate in the "Total Reinvestment
          Plan for Texas Residents" hereinafter described.


    <PAGE>

               Under the Plan (subject to compliance with applicable blue sky
    laws), fractional units ("Plan Units") will be purchased from the Sponsor
    at a price equal to the aggregate offering price per Unit of the bonds in
    the Available Series portfolio during the initial offering of the
    Available Series or at the aggregate bid price per Unit of the Available
    Series if its initial offering has been completed, plus a sales charge
    equal to 3.627% of the net amount invested in such bonds or 3-1/2% of the
    Reinvestment Price per Plan Unit, plus accrued interest, divided by one
    hundred (the "Reinvestment Price per Plan Unit").  All Plan Units will be
    sold at this reduced sales charge of 3-1/2% in comparison to the regular
    sales charge on primary and secondary market sales of Units in any series
    of "Municipal Securities Trust".  Participants in the Plan will have the
    opportunity to designate, in the Authorization Form for the Plan, the name
    of a broker to whom the Sponsor will allocate a sales commission of 1-1/2%
    of the Reinvestment Price per Plan Unit, payable out of the 3-1/2% sales
    charge.  If no such designation is made, the Sponsor will retain the sales
    commission. 

               Under the Plan, the entire amount of a participant's income
    and principal distributions will be reinvested.  For example, a Certifi-
    cateholder who is entitled to receive $130.50 interest income from the
    Trust would acquire 13.05 Plan Units assuming that the Reinvestment Price
    per Plan Unit, plus accrued interest, approximated $10 (Ten Dollars). 

               A semi-annual or annual Certificateholder may join the Plan at
    the time he invests in Units of the Trust or any time thereafter by
    delivering to the Trustee an Authorization Form which is available from
    brokers, any Underwriter of the Units or the Sponsor.  In order that
    distributions may be reinvested on a particular Plan Reinvestment Date,
    the Authorization Form must be received by the Trustee not later than the
    15th day of the month preceding such Date.  Authorization Forms not
    received in time for a particular Plan Reinvestment Date will be valid
    only for the second succeeding Plan Reinvestment Date.  Similarly, a
    participant may withdraw from the program at any time by notifying the
    Trustee (see below).  However, if written confirmation of withdrawal is
    not given to the Trustee prior to a particular distribution, the
    participant will be deemed to have elected to participate in the Plan with
    respect to that particular distribution and his withdrawal would become
    effective for the next succeeding distribution. 

               Once delivered to the Trustee, an Authorization Form will
    constitute a valid election to participate in the Plan with respect to
    Units purchased in the Trust (and with respect to Plan Units purchased
    with the distributions from the Units purchased in the Trust) for each
    subsequent distribution so long as the Certificateholder continues to
    participate in the Plan.  However, if an Available Series should
    materially differ from the Trust in the opinion of the Sponsor, the
    authorization will be voided and participants will be provided with both a
    notice of the material change and a new Authorization Form which would
    have to be returned to the Trustee before the Certificateholder would
    again be able to participate in the Plan.  The Sponsor anticipates that a
    material difference which would result in a voided authorization would
    include such facts as the inclusion of bonds in the Available Series
    portfolio the interest income on which was not exempt from all federal
    income tax, or the inclusion of bonds which were not rated "A" or better
    by Standard & Poor's Corporation or Moody's Investors Service, Inc. on the
    date such bonds were initially deposited in the Available Series
    portfolio. 

               The Sponsor has the option at any time to use units of a
    Secondary Series to fulfill the requirements of the Plan in the event
    units of a Primary Series are not available either because a Primary
    Series is not then in existence or because the registration statement
    relating thereto is not declared effective in sufficient time to
    distribute final prospectuses to Plan participants (see below).  It should
    be noted that there is no assurance that the quality and diversification
    of the Bonds in any Available Series or the estimated current return
    thereon will be similar to that of this Trust. 

               It is the Sponsor's intention that Plan Units will be offered
    on or about each semi-annual and annual Record Date for determining who is
    eligible to receive distributions on the related Payment Date.  Such
    Record Dates are June 1 and December 1 of each year for semi-annual Cer-
    tificateholders, and December 1 of each year for annual Certificate-
    holders.  On each Record Date the Sponsor will send a current Prospectus
    relating to the Available Series being offered for the next Plan
    Reinvestment Date along with a letter which reminds each participant that
    Plan Units are being purchased for him as part of the Plan unless he
    notifies the Trustee in writing by that Plan Reinvestment Date that he no
    longer wishes to participate in the Plan.  In the event a Primary Series
    has not been declared effective in sufficient time to distribute a final
    Prospectus relating thereto and there is no Secondary Series as to which a
    registration statement is currently effective, it is the Sponsor's
    intention to suspend the Plan and distribute to each participant his
    regular semi-annual or annual distribution.  If the Plan is so suspended,
    it will resume in effect with the next Plan Reinvestment Date assuming
    units of an Available Series are then being offered. 

               To aid a participant who might desire to withdraw either from
    the Plan or from a particular distribution, the Trustee has established a
    toll free number (see "Summary of Essential Information" in Part A) for
    participants to use for notification of withdrawal, which must be
    confirmed in writing prior to the Plan Reinvestment Date.  Should the
    Trustee be so notified, it will make the appropriate cash disbursement. 
    Unless the withdrawing participant specifically indicates in his written
    confirmation that (a) he wishes to withdraw from the Plan for that
    particular distribution only, or (b) he wishes to withdraw from the Plan
    for less than all units of each series of "Municipal Securities Trust" or
    "Insured Municipal Securities Trust" which he might then own (and
    specifically identifies which series are to continue in the Plan), he will
    be deemed to have withdrawn completely from the Plan in all respects. 
    Once a participant withdraws completely, he will only be allowed to again
    participate in the Plan by submitting a new Authorization Form.  A sale or
    redemption of a portion of a participant's Plan Units will not constitute
    a withdrawal from the Plan with respect to the remaining Plan Units owned
    by such participant. 

               Unless a Certificateholder notifies the Trustee in writing to
    the contrary, each semi-annual and annual Certificateholder who has
    acquired Plan Units will be deemed to have elected the semi-annual and
    annual plan of distribution, respectively, and to participate in the Plan
    with respect to distributions made in connection with such Plan Units. 
    (Should the Available Series from which Plan Units are purchased for the
    account of an annual Certificateholder fail to have an annual distribution
    plan, such Certificateholder will be deemed to have elected the semi-
    annual plan of distribution, and to participate in the Plan with respect
    to distributions made, in connection with such Plan Units.)  A participant
    who subsequently desires to have distributions made with respect to Plan
    Units delivered to him in cash may withdraw from the Plan with respect to
    such Plan Units and remain in the Plan with respect to units acquired
    other than through the Plan.  Assuming a participant has his distributions
    made with respect to Plan Units reinvested, all such distributions will be
    accumulated with distributions generated from the Units of the Trust used
    to purchase such additional Plan Units.  However, distributions related to
    units in other series of "Municipal Securities Trust" will not be
    accumulated with the foregoing distributions for Plan purchases.  Thus, if
    a person owns units in more than one series of "Municipal Securities
    Trust" (which are not the result of purchases under the Plan),
    distributions with respect thereto will not be aggregated for purchases
    under the Plan. 

               Although not obligated to do so, the Sponsor intends to
    maintain a market for the Plan Units and continuously to offer to purchase
    Plan Units at prices based upon the aggregate offering price of the Bonds
    in the Available Series portfolio during the initial offering of the
    Available Series, or at the aggregate bid price of the Bonds of the
    Available Series after its initial offering has been completed.  The
    Sponsor may discontinue such purchases at any time.  The aggregate bid
    price of the underlying bonds may be expected to be less than the
    aggregate offering price.  In the event that a market is not maintained
    for Plan Units, a participant desiring to dispose of his Plan Units may be
    able to do so only by tendering such Plan Units to the Trustee for
    redemption at the Redemption Price of the full units in the Available
    Series corresponding to such Plan Units, which is based upon the aggregate
    bid price of the underlying bonds as described in the "Insured Municipal
    Securities Trust" Prospectus for the Available Series in question.  If a
    participant wishes to dispose of his Plan Units, he should inquire of the
    Sponsor as to current market prices prior to making a tender for
    redemption to the Trustee. 

               Any participant may tender his Plan Units for redemption to
    the Available Series Trust.  Participants may redeem Plan Units by making
    a written request to the Trustee, at the address listed in the "Summary of
    Essential Information" in Part A, on the Redemption Form supplied by the
    Trustee.  The redemption price per Plan Unit will be determined as set
    forth in the "Insured Municipal Securities Trust" Prospectus of the
    Available Series from which such Plan Unit was purchased following receipt
    of the request and adjusted to reflect the fact that it relates to a Plan
    Unit.  There is no charge for the redemption of Plan Units. 

               The Trust Agreement requires that the Trustee notify the
    Sponsor of any tender of Plan Units for redemption.  So long as the
    Sponsor is maintaining a bid in the secondary market, the Sponsor will
    purchase any Plan Units tendered to the Trustee for redemption by making
    payment therefor to the Certificateholder in an amount not less than the
    redemption price for such Plan Units on the date of tender not later than
    the day on which such Plan Units otherwise would have been redeemed by the
    Trustee. 

               Participants in the Plan will not receive individual
    certificates for their Plan Units unless the amount of Plan Units
    accumulated represents $1,000 principal amount of bonds underlying such
    Units and, in such case, a written request for certificates is made to the
    Trustee.  All Plan Units will be accounted for by the Trustee on a book
    entry system.  Each time Plan Units are purchased under the Plan, a
    participant will receive a confirmation stating his cost, number of Units
    purchased and estimated current return.  Questions regarding a
    participant's statements should be directed to the Trustee by calling the
    Trustee at the number set forth under "Summary of Essential Information"
    in Part A of this Prospectus.

               All expenses relating to the operation of the Plan will be
    borne by the Sponsor.  The Sponsor and the Trustee reserve the right to
    suspend, modify or terminate the Plan at any time for any reason,
    including the right to suspend the Plan if the Sponsor is unable or
    unwilling to establish a Primary Series or is unable to provide Secondary
    Series Units.  All participants will receive notice of any such
    suspension, modification or termination. 

    Total Reinvestment Plan For Texas Residents

               Except as specifically provided under this section, and unless
    the context otherwise requires, all provisions and definitions contained
    under the heading "Total Reinvestment Plan" shall be applicable to the
    Total Reinvestment Plan for Texas Residents ("Texas Plan"). 

               Semi-annual and annual Certificateholders of the Trust who are
    residents of Texas have the option prior to any semi-annual or annual
    distribution to affirmatively elect to reinvest that distribution,
    including both interest and principal, if any, in an Available Series. 

               A resident of Texas who is a semi-annual or annual Certifi-
    cateholder may join the Texas Plan for any particular semi-annual or
    annual distribution by delivering to the Trustee an Authorization Form For
    Texas Residents ("Texas Authorization Form") specifically mentioning the
    date of the particular semi-annual or annual distribution he wishes to
    reinvest. On or about each semi-annual or annual Record Date, Texas
    Authorization Forms shall be sent by the Trustee to every Certificate-
    holder who, according to the Trustee's records, is a resident of Texas. 
    In the event that the Sponsor suspends the Plan or the Texas Plan no Texas
    Authorization Forms shall be sent.  In order that distributions may be
    reinvested on a particular Plan Reinvestment Date, the Texas Authorization
    Form must be received by the Trustee on or before such Date.  Texas
    Authorization Forms not received in time for the Plan Reinvestment Date
    will be deemed void.  A participant who delivers a Texas Authorization
    Form to the Trustee may thereafter withdraw said authorization by
    notifying the Trustee at its toll free telephone number prior to a Plan
    Reinvestment Date.  Such notification of withdrawal must be confirmed in
    writing prior to the Plan Reinvestment Date.  Under no circumstances shall
    a Texas Authorization Form be provided or accepted by the Trustee which
    provides for the reinvestment of distributions for more than one Plan
    Reinvestment Date. 

               On or about each semi-annual and annual Record Date, the
    Sponsor will send a current Prospectus relating to the Available Series
    being offered on the next Plan Reinvestment Date along with a letter
    incorporating a Texas Authorization Form which specifies the funds
    available for reinvestment, reminds each participant that no Plan Units
    will be purchased for him unless the Texas Authorization Form is received
    by the Trustee on or before that particular Plan Reinvestment Date, and
    states that the Texas Authorization Form is valid only for that particular
    semi-annual or annual distribution.  If the Available Series should
    materially differ from the Trust, the participant will be provided with a
    notice of the material change and a new Texas Authorization Form which
    would have to be returned to the Trustee before the Certificateholder
    would again be able to participate in the Plan. 

               Each semi-annual and annual Certificateholder who has acquired
    Plan Units will be deemed to have elected the semi-annual and annual plan
    of distribution, respectively, with respect to such Units, but such Cer-
    tificateholder will not be deemed to participate in the Plan for any
    particular distribution unless and until he delivers to the Trustee a
    Texas Authorization Form pertaining to those Plan Units.  (Should the
    Available Series from which Plan Units are purchased for the account of an
    annual Certificateholder fail to have an annual distribution plan, such
    Certificateholder will be deemed to have elected the semi-annual plan of
    distribution, and to participate in the Plan with respect to distributions
    made in connection with such Plan Units.)


                               TRUST ADMINISTRATION

    Portfolio Supervision

               Except for the purchase of Replacement Bonds or as discussed
    herein, the acquisition of any Bonds for the Trust other than Bonds
    initially deposited by the Sponsor is prohibited.  Although it is the
    Sponsor's and Trustee's intention not to dispose of Bonds insured pursuant
    to the Bond Insurance in the event of default, nevertheless, the Sponsor
    may direct the Trustee to dispose of Bonds upon (i) default in payment of
    principal or interest on such Bonds, (ii) institution of certain legal
    proceedings with respect to the issuers of such Bonds, (iii) default under
    other documents adversely affecting debt service on such Bonds,
    (iv) default in payment of principal or interest on other obligations of
    the same issuer or guarantor, (v) with respect to revenue Bonds, decline
    in revenues and income of any facility or project below the estimated
    levels calculated by proper officials charged with the construction or
    operation of such facility or project or (vi) decline in price or the
    occurrence of other market or credit factors that in the opinion of the
    Sponsor would make the retention of such Bonds in the Trust detrimental to
    the interests of the Certificateholders.  If a default in the payment of
    principal or interest on any of the Bonds occurs and if the Sponsor fails
    to instruct the Trustee to sell or hold such Bonds, the Trust Agreement
    provides that the Trustee may sell such Bonds.  The Trustee shall not be
    liable for any depreciation or loss by reason of any sale of bonds or by
    reason of the failure of the Sponsor to give directions to the Trustee. 

               The Sponsor is authorized by the Trust Agreement to direct the
    Trustee to accept or reject certain plans for the refunding or refinancing
    of any of the Bonds.  Any bonds received in exchange or substitution will
    be held by the Trustee subject to the terms and conditions of the
    Agreement to the same extent as the Bonds originally deposited.  Within
    five days after such deposit, notice of such exchange and deposit shall be
    given by the Trustee to each Certificateholder registered on the books of
    the Trustee, including an identification of the Bonds eliminated and the
    Bonds substituted therefor. 

    Trust Agreement, Amendment And Termination

               The Trust Agreement may be amended by the Trustee, the Sponsor
    and the Evaluator without the consent of any of the Certificateholders: 
    (1) to cure any ambiguity or to correct or supplement any provision which
    may be defective or inconsistent; (2) to change any provision thereof as
    may be required by the Securities and Exchange Commission or any successor
    governmental agency; or (3) to make such other provisions in regard to
    matters arising thereunder as shall not adversely affect the interests of
    the Certificateholders. 

               The Trust Agreement may also be amended in any respect, or
    performance of any of the provisions thereof may be waived, with the
    consent of the holders of Certificates evidencing 66-2/3% of the Units
    then outstanding for the purpose of modifying the rights of Certificate-
    holders; provided that no such amendment or waiver shall reduce any Cer-
    tificateholder's interest in the Trust without his consent or reduce the
    percentage of Units required to consent to any such amendment or waiver
    without the consent of the holders of all Certificates.  The Trust
    Agreement may not be amended, without the consent of the holders of all
    Certificates then outstanding, to increase the number of Units issuable or
    to permit the acquisition of any bonds in addition to or in substitution
    for those initially deposited in the Trust, except in accordance with the
    provisions of the Trust Agreement.  The Trustee shall promptly notify Cer-
    tificateholders, in writing, of the substance of any such amendment. 

               The Trust Agreement provides that the Trust shall terminate
    upon the maturity, redemption or other disposition, as the case may be, of
    the last of the Bonds held in the Trust but in no event is it to continue
    beyond the end of the calendar year preceding the fiftieth anniversary of
    the execution of the Trust Agreement.  If the value of the Trust shall be
    less than the minimum amount set forth under "Summary of Essential
    Information" in Part A, the Trustee may, in its discretion, and shall when
    so directed by the Sponsor, terminate the Trust.  The Trust may also be
    terminated at any time with the consent of the holders of Certificates
    representing 100% of the Units then outstanding.  In the event of
    termination, written notice thereof will be sent by the Trustee to all
    Certificateholders.  Within a reasonable period after termination, the
    Trustee must sell any Bond remaining in the Trust, and, after paying all
    expenses and charges incurred by the Trust, distribute to each Certifi-
    cateholder, upon surrender for cancellation of his Certificate for Units,
    his pro rata share of the Interest and Principal Accounts. 

    The Sponsor

       
               The Sponsor, Bear, Stearns & Co. Inc., a Delaware corporation,
    is engaged in the underwriting, investment banking and brokerage business
    and is a member of the National Association of Securities Dealers, Inc.
    and all principal securities and commodities exchanges, including the New
    York Stock Exchange, the American Stock Exchange, the Midwest Stock
    Exchange and the Pacific Stock Exchange.  Bear Stearns maintains its
    principal business offices at 245 Park Avenue, New York, New York 10167
    and, since its reorganization from a partnership to a corporation in
    October, 1985 has been a wholly-owned subsidiary of The Bear Stearns
    Companies Inc.  Bear Stearns, through its predecessor entities, has been
    engaged in the investment banking and brokerage business since 1923.  Bear
    Stearns is the sponsor for numerous series of unit investment trusts,
    including:  A Corporate Trust, Series 1 (and Subsequent Series); New York
    Municipal Trust, Series 1 (and Subsequent Series), Discount and Zero
    Coupon Fund, 1st Series (and Subsequent Series); Municipal Securities
    Trust, Series 1 (and Subsequent Series), 1st Discount Series (and
    Subsequent Series); High Income Series 1 (and Subsequent Series); Multi-
    State Series 1 (and Subsequent Series); Insured Municipal Securities
    Trust, Series 1-4 (Multiplier Portfolio), Series 1 (and Subsequent
    Series), 5th Discount Series (and Subsequent Series), Navigator Series
    (and Subsequent Series); Mortgage Securities Trust, CMO Series 1 (and
    Subsequent Series) and Equity Securities Trust, Series 1, Signature
    Series, Gabelli Communications Income Trust (and Subsequent Series).  The
    information included herein is only for the purpose of informing investors
    as to the financial responsibility of the Sponsor and its ability to carry
    out its contractual obligations. 
        

               The Sponsor is liable for the performance of its obligations
    arising from its responsibilities under the Trust Agreement, but will be
    under no liability to Certificateholders for taking any action, or
    refraining from taking any action, in good faith pursuant to the Trust
    Agreement, or for errors in judgment except in cases of its own willful
    misfeasance, bad faith, gross negligence or reckless disregard of its
    obligations and duties. 

               The Sponsor may resign at any time by delivering to the
    Trustee an instrument of resignation executed by the Sponsor. 

               If at any time the Sponsor shall resign or fail to perform any
    of its duties under the Trust Agreement or becomes incapable of acting or
    becomes bankrupt or its affairs are taken over by public authorities, then
    the Trustee may either (a) appoint a successor Sponsor; (b) terminate the
    Trust Agreement and liquidate the Trust; or (c) continue to act as Trustee
    without terminating the Trust Agreement.  Any successor Sponsor appointed
    by the Trustee shall be satisfactory to the Trustee and, at the time of
    appointment, shall have a net worth of at least $1,000,000. 

    The Trustee

               For certain of the Trusts as set forth in the "Summary of
    Essential Information" in Part A, the Trustee is United States Trust
    Company of New York, with its principal place of business at 45 Wall
    Street, New York, New York 10005 and a corporate trust office at 770
    Broadway, New York, New York 10003.  United States Trust Company of New
    York has, since its establishment in 1853, engaged primarily in the
    management of trust and agency accounts for individuals and corporations. 
    The Trustee is a member of the New York Clearing House Association and is
    subject to supervision and examination by the Superintendent of Banks of
    the State of New York, the Federal Deposit Insurance Corporation and the
    Board of Governors of the Federal Reserve System.

               For certain other Trusts as set forth in the "Summary of
    Essential Information" in Part A, the Trustee is The Bank of New York, a
    trust company organized under the laws of New York, having its offices at
    101 Barclay Street, New York, New York 10286 (1-800-431-8002).  The Bank
    of New York is subject to supervision and examination by the
    Superintendent of Banks of the State of New York and the Board of
    Governors of the Federal Reserve System, and its deposits are insured by
    the Federal Deposit Insurance Corporation to the extent permitted by law. 
    The Trustee must be a banking corporation organized under the laws of the
    United States or any state which is authorized under such laws to exercise
    corporate trust powers and must have at all times an aggregate capital,
    surplus and undivided profits of not less than $5,000,000.  The duties of
    the Trustee are primarily ministerial in nature.  The Trustee did not
    participate in the selection of Securities for the portfolio of the Trust.

               The Trustee shall not be liable or responsible in any way for
    taking any action, or for refraining from taking any action, in good faith
    pursuant to the Trust Agreement, or for errors in judgment; or for any
    disposition of any moneys, bonds or Certificates in accordance with the
    Trust Agreement, except in cases of its own willful misfeasance, bad
    faith, gross negligence or reckless disregard of its obligations and
    duties; provided, however, that the Trustee shall not in any event be
    liable or responsible for any evaluation made by the Evaluator.  In
    addition, the Trustee shall not be liable for any taxes or other
    governmental charges imposed upon or in respect of the Bonds or the Trust
    which it may be required to pay under current or future law of the United
    States or any other taxing authority having jurisdiction.  The Trustee
    shall not be liable for depreciation or loss incurred by reason of the
    sale by the Trustee of any of the Bonds pursuant to the Trust Agreement. 

               For further information relating to the responsibilities of
    the Trustee under the Trust Agreement, reference is made to the material
    set forth under "Rights of Certificateholders".

               The Trustee may resign by executing an instrument in writing
    and filing the same with the Sponsor, and mailing a copy of a notice of
    resignation to all Certificateholders.  In such an event the Sponsor is
    obligated to appoint a successor Trustee as soon as possible.  In
    addition, if the Trustee becomes incapable of acting or becomes bankrupt
    or its affairs are taken over by public authorities, the Sponsor may
    remove the Trustee and appoint a successor as provided in the Trust
    Agreement.  Notice of such removal and appointment shall be mailed to each
    Certificateholder by the Sponsor.  If upon resignation of the Trustee no
    successor has been appointed and has accepted the appointment within
    thirty days after notification, the retiring Trustee may apply to a court
    of competent jurisdiction for the appointment of a successor.  The
    resignation or removal of the Trustee becomes effective only when the
    successor Trustee accepts its appointment as such or when a court of
    competent jurisdiction appoints a successor Trustee. Upon execution of a
    written acceptance of such appointment by such successor Trustee, all the
    rights, powers, duties and obligations of the original Trustee shall vest
    in the successor. 

               Any corporation into which the Trustee may be merged or with
    which it may be consolidated, or any corporation resulting from any merger
    or consolidation to which the Trustee shall be a party, shall be the
    successor Trustee.  The Trustee must always be a banking corporation
    organized under the laws of the United States or any State and have at all
    times an aggregate capital, surplus and undivided profits of not less than
    $2,500,000. 

    The Evaluator

               The Evaluator is Kenny S&P Evaluation Services, a division of
    Kenny Information Systems, Inc. with main offices located at 65 Broadway,
    New York, New York 10006.  The Evaluator is a wholly-owned subsidiary of
    McGraw-Hill Inc.  The Evaluator is a registered investment advisor and
    also provides financial information services. 

               The Trustee, the Sponsor and the Certificateholders may rely
    on any evaluation furnished by the Evaluator and shall have no
    responsibility for the accuracy thereof.  Determinations by the Evaluator
    under the Trust Agreement shall be made in good faith upon the basis of
    the best information available to it, provided, however, that the
    Evaluator shall be under no liability to the Trustee, the Sponsor or Cer-
    tificateholders for errors in judgment, except in cases of its own willful
    misfeasance, bad faith, gross negligence or reckless disregard of its
    obligations and duties. 

               The Evaluator may resign or may be removed by the Sponsor and
    Trustee, and the Sponsor and the Trustee are to use their best efforts to
    appoint a satisfactory successor. Such resignation or removal shall become
    effective upon the acceptance of appointment by the successor Evaluator. 
    If upon resignation of the Evaluator no successor has accepted appointment
    within thirty days after notice of resignation, the Evaluator may apply to
    a court of competent jurisdiction for the appointment of a successor. 


                            TRUST EXPENSES AND CHARGES


               At no cost to the Trust, the Sponsor has borne all the
    expenses of creating and establishing the Trust, including the cost of
    initial preparation and execution of the Trust Agreement, registration of
    the Trust and the Units under the Investment Company Act of 1940 and the
    Securities Act of 1933, the premiums on the Sponsor-Insured Bonds, initial
    preparation and printing of the Certificates, the fees of the Evaluator
    during the initial public offering, legal expenses, advertising and
    selling expenses, expenses of the Trustee including, but not limited to,
    an amount equal to interest accrued on certain "when issued" bonds since
    the date of settlement for the Units, initial fees and other out-of-pocket
    expenses. 

               The Sponsor will not charge the Trust a fee for its services
    as such.  (See "Sponsor's Profits".)

               The Sponsor will receive for portfolio supervisory services to
    the Trust an Annual Fee in the amount set forth under "Summary of
    Essential Information" in Part A of this Prospectus.  The Sponsor's fee
    may exceed the actual cost of providing portfolio supervisory services for
    this Trust, but at no time will the total amount received for portfolio
    supervisory services rendered to all series of the Municipal Securities
    Trust in any calendar year exceed the aggregate cost to the Sponsor of
    supplying such services in such year. (See "Portfolio Supervision".)

               The Trustee will receive for its ordinary recurring services
    to the Trust an annual fee in the amount set forth under "Summary of
    Essential Information" in Part A of this Prospectus.  For a discussion of
    the services performed by the Trustee pursuant to its obligations under
    the Trust Agreement, see "Trust Administration" and "Rights of Certifi-
    cateholders".

               The Evaluator will receive, for each daily evaluation of the
    Bonds in the Trust after the initial public offering is completed, a fee
    in the amount set forth under "Summary of Essential Information" in Part A
    of this Prospectus. 

               The Trustee's and Evaluator's fees are payable monthly as of
    the Record Date from the Interest Account to the extent funds are
    available and then from the Principal Account.  Both fees may be increased
    without approval of the Certificateholders by amounts not exceeding
    proportionate increases in consumer prices for services as measured by the
    United States Department of Labor's Consumer Price Index entitled "All
    Services Less Rent".

               The following additional charges are or may be incurred by the
    Trust:  all expenses (including counsel fees) of the Trustee incurred and
    advances made in connection with its activities under the Trust Agreement,
    including the expenses and costs of any action undertaken by the Trustee
    to protect the Trust and the rights and interests of the Certificate-
    holders; fees of the Trustee for any extraordinary services performed
    under the Trust Agreement; indemnification of the Trustee for any loss or
    liability accruing to it without gross negligence, bad faith or willful
    misconduct on its part, arising out of or in connection with its
    acceptance or administration of the Trust; indemnification of the Sponsor
    for any losses, liabilities and expenses incurred in acting as Sponsor of
    the Trust without gross negligence, bad faith or willful misconduct on its
    part; and all taxes and other governmental charges imposed upon the Bonds
    or any part of the Trust (no such taxes or charges are being levied, made
    or, to the knowledge of the Sponsor, contemplated).  The above expenses,
    including the Trustee's fees, when paid by or owing to the Trustee are
    secured by a first lien on the Trust.  In addition, the Trustee is
    empowered to sell Bonds in order to make funds available to pay all
    expenses. 

               The accounts of the Trust shall be audited not less than
    annually by independent public accountants selected by the Sponsor.  So
    long as the Sponsor maintains a secondary market, the Sponsor will bear
    any audit expense which exceeds 50 cents per Unit.  Certificateholders
    covered by the audit during the year may receive a copy of the audited
    financial upon request. 


                      EXCHANGE PRIVILEGE AND CONVERSION OFFER

    Exchange Privilege

               Certificateholders may elect to exchange any or all of their
    Units of these Trusts for Units of one or more of any available series of
    Insured Municipal Securities Trust, Municipal Securities Trust, New York
    Municipal Trust, Mortgage Securities Trust, A Corporate Trust or Equity
    Securities Trust (upon receipt by the Equity Securities Trust of an
    appropriate exemptive order from the Securities & Exchange Commission)
    (the "Exchange Trusts") at a reduced sales charge as set forth below. 
    Under the Exchange Privilege, the Sponsor's repurchase price of the Units
    being surrendered, and only after the initial offering period has been
    completed, will be based on the aggregate bid price of the Bonds in the
    particular Trust portfolio.  Units in an Exchange Trust then will be sold
    to the Certificateholder at a price based on the aggregate offer price of
    the Bonds in the Exchange Trust portfolio (or for Units of Equity
    Securities Trust, based on the market value of the underlying securities
    in the Equity Trust portfolio) during the initial public offering period
    of the Exchange Trust; or, based on the aggregate bid price of the Bonds
    in the Exchange Trust portfolio if its initial public offering has been
    completed, plus accrued interest (or for Units of Equity Securities Trust,
    based on the market value of the underlying securities in the Equity Trust
    portfolio) and a reduced sales charge as set forth below.

               Except for unitholders who wish to exercise the Exchange
    Privilege within the first five months of their purchase of Units of
    Trust, the sales charge applicable to the purchase of units of an Exchange
    Trust shall be $15 per unit (or per 1,000 units for the Mortgage
    Securities Trust or per 100 Units for the Equity Securities Trust)
    (approximately 1.5% of the price of each Exchange Trust unit (or 1,000
    Units for the Mortgage Securities Trust or per 100 Units for the Equity
    Securities Trust)).  For unitholders who wish to exercise the Exchange
    Privilege within the first five months of their purchase of Units of
    Trust, the sales charge applicable to the purchase of units of an Exchange
    Trust shall be the greater of (i) $15 per unit (or per 1,000 Units for the
    Mortgage Securities Trust or per 100 Units for the Equity Securities
    Trust), or (ii) an amount which when coupled with the sales charge paid by
    the unitholder upon his original purchase of Units of the Trust at least
    equals the sales charge applicable in the direct purchase of units of an
    Exchange Trust.  The Exchange Privilege is subject to the following
    conditions:

               (1)  The Sponsor must be maintaining a secondary market in
          both the Units of the Trust held by the Certificateholder and the
          Units of the available Exchange Trust.  While the Sponsor has
          indicated its intention to maintain a market in the Units of all
          Trusts sponsored by it, the Sponsor is under no obligation to
          continue to maintain a secondary market and therefore there is no
          assurance that the Exchange Privilege will be available to a
          Certificateholder at any specific time in the future.  At the time
          of the Certificateholder's election to participate in the Exchange
          Privilege, there also must be Units of the Exchange Trust available
          for sale, either under the initial primary distribution or in the
          Sponsor's secondary market.

               (2)  Exchanges will be effected in whole units only.  Any
          excess proceeds from the Units surrendered for exchange will be
          remitted and the selling Certificateholder will not be permitted to
          advance any new funds in order to complete an exchange.  Units of
          the Mortgage Securities Trust may only be acquired in blocks of
          1,000 Units.  Units of the Equity Securities Trust may only be
          acquired in blocks of 100 Units.

               (3)  The Sponsor reserves the right to suspend, modify or
          terminate the Exchange Privilege.  The Sponsor will provide
          unitholders of the Trust with 60 days' prior written notice of any
          termination or material amendment to the Exchange Privilege,
          provided that, no notice need be given if (i) the only material
          effect of an amendment is to reduce or eliminate the sales charge
          payable at the time of the exchange, to add one or more series of
          the Trust eligible for the Exchange Privilege or to delete a series
          which has been terminated from eligibility for the Exchange
          Privilege, (ii) there is a suspension of the redemption of units of
          an Exchange Trust under Section 22(e) of the Investment Company Act
          of 1940, or (iii) an Exchange Trust temporarily delays or ceases the
          sale of its units because it is unable to invest amounts effectively
          in accordance with its investment objectives, policies and
          restrictions.  During the 60 day notice period prior to the
          termination or material amendment of the Exchange Privilege
          described above, the Sponsor will continue to maintain a secondary
          market in the units of all Exchange Trusts that could be acquired by
          the affected unitholders.  Unitholders may, during this 60 day
          period, exercise the Exchange Privilege in accordance with its terms
          then in effect.  In the event the Exchange Privilege is not
          available to a Certificateholder at the time he wishes to exercise
          it, the Certificateholder will immediately be notified and no action
          will be taken with respect to his Units without further instructions
          from the Certificateholder.

               To exercise the Exchange Privilege, a Certificateholder should
    notify the Sponsor of his desire to exercise his Exchange Privilege.  If
    Units of a designated, outstanding series of an Exchange Trust are at the
    time available for sale and such Units may lawfully be sold in the state
    in which the Certificateholder is a resident, the Certificateholder will
    be provided with a current prospectus or prospectuses relating to each
    Exchange Trust in which he indicates an interest.  He may then select the
    Trust or Trusts into which he desires to invest the proceeds from his sale
    of Units.  The exchange transaction will operate in a manner essentially
    identical to a secondary market transaction except that units may be
    purchased at a reduced sales charge.

               Example:  Assume that after the initial public offering has
    been completed, a Certificateholder has five units of a Trust with a
    current value of $700 per unit which he has held for more than 5 months
    and the Certificateholder wishes to exchange the proceeds for units of a
    secondary market Exchange Trust with a current price of $725 per unit. 
    The proceeds from the Certificateholder's original units will aggregate
    $3,500.  Since only whole units of an Exchange Trust may be purchased
    under the Exchange Privilege, the Certificateholder would be able to
    acquire four units (or 4,000 Units of the Mortgage Securities Trust or 400
    Units of the Equity Securities Trust) for a total cost of $2,960 ($2,900
    for unit and $60 for the sales charge).  The remaining $540 would be
    remitted to the Certificateholder in cash.  If the Certificateholder
    acquired the same number of units at the same time in a regular secondary
    market transaction, the price would have been $3,068.80 ($2,900 for units
    and $168.80 for the sales charge, assuming a 5 1/2% sales charge times the
    public offering price).

    The Conversion Offer

               Unit owners of any registered unit investment trust for which
    there is no active secondary market in the units of such trust (a
    "Redemption Trust") may elect to redeem such units and apply the proceeds
    of the redemption to the purchase of available Units of one or more series
    of A Corporate Trust, Municipal Securities Trust, Insured Municipal
    Securities Trust, Mortgage Securities Trust, New York Municipal Trust or
    Equity Securities Trust (upon receipt by the Equity Securities Trust of an
    appropriate exemptive order from the Securities and Exchange Commission)
    sponsored by Bear, Stearns & Co. Inc. or the Sponsor (the "Conversion
    Trusts") at the Public Offering Price for units of the Conversion Trust
    based on a reduced sales charge as set forth below.  Under the Conversion
    Offer, units of the Redemption Trust must be tendered to the trustee of
    such trust for redemption at the redemption price, which is based upon the
    aggregate bid side evaluation of the underlying bonds in such trust and is
    generally about 1-1.2% to 2% lower than the offering price for such bonds
    (or for Units of Equity Securities Trust, based on the market value of the
    underlying securities in the Equity Trust portfolio).  The purchase price
    of the Units will be based on the aggregate offer price of the Bonds in
    the Conversion Trust portfolio (or for Units of Equity Securities Trust,
    based on the market value of the underlying securities in the Equity Trust
    portfolio) during the public offering of the Conversion Trust; or, based
    on the aggregate bid price of the underlying bonds if the initial public
    offering of the Conversion Trust has been completed, plus accrued interest
    (or for Units of Equity Securities Trust, based on the market value of the
    underlying securities in the Equity Trust portfolio) and a sales charge as
    set forth below.

               Except for unitholders who wish to exercise the Conversion
    Offer within the first five months of their purchase of units of a
    Redemption Trust, the sales charge applicable to the purchase of Units of
    the Conversion Trust shall be $15 per Unit (or per 1,000 Units for the
    Mortgage Securities Trust or per 100 Units for the Equity Securities
    Trust).  For unitholders who wish to exercise the Conversion Offer within
    the first five months of their purchase of units of a Redemption Trust,
    the sales charge applicable to the purchase of Units of a Conversion Trust
    shall be the greater of (i) $15 per Unit (or per 1,000 Units for the
    Mortgage Securities Trust or per 100 Units for the Equity Securities
    Trust) or (ii) an amount which when coupled with the sales charge paid by
    the unitholder upon his original purchase of units of the Redemption Trust
    at least equals the sales charge applicable in the direct purchase of
    Units of a Conversion Trust.  The Conversion Offer is subject to the
    following limitations:

               (1)  The Conversion Offer is limited only to unit owners of
          any Redemption Trust, defined as a unit investment trust for which
          there is no active secondary market at the time the
          Certificateholder elects to participate in the Conversion Offer.  At
          the time of the unit owner's election to participate in the
          Conversion Offer, there also must be available units of a Conversion
          Trust, either under a primary distribution or in the Sponsor's
          secondary market.

               (2)  Exchanges under the Conversion Offer will be effected in
          whole units only.  Unit owners will not be permitted to advance any
          new funds in order to complete an exchange under the Conversion
          Offer.  Any excess proceeds from units being redeemed will be
          returned to the unit owner.  Units of the Mortgage Securities Trust
          may only be acquired in blocks of 1,000 Units.  Units of the Equity
          Securities Trust may only be acquired in blocks of 100 Units.

               (3)  The Sponsor reserves the right to modify, suspend or
          terminate the Conversion Offer at any time without notice to unit
          owners of Redemption Trusts.  In the event the Conversion Offer is
          not available to a unit owner at the time he wishes to exercise it,
          the unit owner will be notified immediately and no action will be
          taken with respect to his units without further instruction from the
          unit owner.  The Sponsor also reserves the right to raise the sales
          charge based on actual increases in the Sponsor's costs and expenses
          in connection with administering the program, up to a maximum sales
          charge of $20 per unit (or per 1,000 units for the Mortgage
          Securities Trust or per 100 units for the Equity Securities Trust).

               To exercise the Conversion Offer, a unit owner of a Redemption
    Trust should notify his retail broker of his desire to redeem his
    Redemption Trust Units and use the proceeds from the redemption to
    purchase Units of one or more of the Conversion Trusts.  If Units of a
    designated, outstanding series of a Conversion Trust are at that time
    available for sale and if such Units may lawfully be sold in the state in
    which the unit owner is a resident, the unit owner will be provided with a
    current prospectus or prospectuses relating to each Conversion Trust in
    which he indicates an interest.  He then may select the Trust or Trusts
    into which he decides to invest the proceeds from the sale of his Units. 
    The transaction will be handled entirely through the unit owner's retail
    broker.  The retail broker must tender the units to the trustee of the
    Redemption Trust for redemption and then apply the proceeds to the
    redemption toward the purchase of units of a Conversion Trust at a price
    based on the aggregate offer or bid side evaluation per Unit of the
    Conversion Trust, depending on which price is applicable, plus accrued
    interest and the applicable sales charge.  The certificates must be
    surrendered to the broker at the time the redemption order is placed and
    the broker must specify to the Sponsor that the purchase of Conversion
    Trust Units is being made pursuant to the Conversion Offer.  The unit
    owner's broker will be entitled to retain $5 of the applicable sales
    charge.

               Example:  Assume a unit owner has five units of a Redemption
    Trust which has held for more than 5 months with a current redemption
    price of $675 per unit based on the aggregate bid price of the underlying
    bonds and the unit owner wishes to participate in the Conversion Offer and
    exchange the proceeds for units of a secondary market Conversion Trust
    with a current price of $750 per Unit.  The proceeds from the unit owner's
    redemption of units will aggregate $3,375.  Since only whole units of a
    Redemption Trust may be purchased under the Conversion Offer, the unit
    owner will be able to acquire four units of the Conversion Trust (or 4,000
    Units of the Mortgage Securities Trust or 400 Units of the Equity
    Securities Trust) for a total cost of $2,860 ($2,800 for units and $60 for
    the sales charge).  The remaining $515 would be remitted to the unit owner
    in cash.  If the unit owner acquired the same number of Conversion Trust
    units at the same time in a regular secondary market transaction, the
    price would have been $2,962.96 ($2,800 for units and $162.96 sales
    charge, assuming a 5 1/2% sales charge times the public offering price).

    Description of the Exchange Trusts and the Conversion Trusts

               A Corporate Trust may be an appropriate investment vehicle for
    an investor who is more interested in a higher current return on his
    investment (although taxable) than a tax-exempt return (resulting from the
    fact that the current return from taxable fixed income securities is
    normally higher than that available from tax-exempt fixed income
    securities).  Municipal Securities Trust and New York Municipal Trust may
    be appropriate investment vehicles for an investor who is more interested
    in tax-exempt income.  The interest income from New York Municipal Trust
    is, in general, also exempt from New York State and local New York income
    taxes, while the interest income from Municipal Securities Trust is
    subject to applicable New York State and local New York taxes, except for
    that portion of the income which is attributable to New York obligations
    in the Trust portfolio, if any.  The interest income from each State Trust
    of the Municipal Securities Trust, Multi-State Series is, in general,
    exempt from state and local taxes when held by residents of the state
    where the issuers of bonds in such State Trusts are located.  The Insured
    Municipal Securities Trust combines the advantages of providing interest
    income free from regular federal income tax under existing law with the
    added safety of irrevocable insurance on the underlying obligations. 
    Insured Navigator Series further combines the advantages of providing
    interest income free from regular federal income tax and state and local
    taxes when held by residents of the state where issuers of bonds in such
    state trusts are located with the added safety of irrevocable insurance on
    the underlying obligations.  Mortgage Securities Trust offers an
    investment vehicle for investors who are interested in obtaining safety of
    capital and a high level of current distribution of interest income
    through investment in a fixed portfolio of collateralized mortgage
    obligations.  Equity Securities Trust offers investors an opportunity to
    achieve capital appreciation together with a high level of current income.

    Tax Consequences of the Exchange Privilege and the Conversion Offer

       
               A surrender of Units pursuant to the Exchange Privilege or the
    Conversion Offer will constitute a "taxable event" to the Certificate-
    holder under the Code.  The Certificateholder will realize a tax gain or
    loss that will be of a long- or short-term capital or ordinary income
    nature depending on the length of time the Units have been held and other
    factors.  A Certificateholder's tax basis in the Units acquired pursuant
    to the Exchange Privilege or Conversion Offer will be equal to the
    purchase price of such Units.  Investors should consult their own tax
    advisors as to the tax consequences to them of exchanging or redeeming
    units and participating in the Exchange Privilege or Conversion Offer. 
        

                                   OTHER MATTERS

    Legal Opinions

               The legality of the Units offered hereby and certain matters
    relating to federal tax law have been passed upon by Messrs. Battle
    Fowler, 280 Park Avenue, New York, New York 10017 as counsel for the
    Sponsor.  Messrs. Carter, Ledyard & Milburn, Two Wall Street, New York,
    New York 10005 have acted as counsel for United States Trust Company of
    New York.  On the initial date of deposit, Messrs. Booth & Baron, 122 East
    42nd Street, New York, New York 10168 acted as counsel for The Bank of New
    York. 

    Independent Auditors

               The financial statements of the Trust included in Part A of
    this Prospectus as of the dates set forth in Part A, have been examined by
    KPMG Peat Marwick, independent certified public accountants, for the
    periods indicated in its reports appearing herein.  The financial
    statements examined by KPMG Peat Marwick have been so included in reliance
    on its report given upon the authority of said firm as experts in 
    accounting and auditing. 


                           DESCRIPTION OF BOND RATINGS*

    Standard & Poor's Corporation

               A brief description of the applicable Standard & Poor's
    Corporation rating symbols and their meanings is as follows: 

               A Standard & Poor's corporate or municipal bond rating is a
    current assessment of the creditworthiness of an obligor with respect to a
    specific debt obligation.  This assessment of creditworthiness may take
    into consideration obligors such as guarantors, insurers, or lessees. 

               The bond rating is not a recommendation to purchase or sell a
    security, inasmuch as it does not comment as to market price. 

               The ratings are based on current information furnished to
    Standard & Poor's by the issuer and obtained by Standard & Poor's from
    other sources it considers reliable.  The ratings may be changed,
    suspended or withdrawn as a result of changes in, or unavailability of,
    such information. 

    *     As described by the rating agencies.


    <PAGE>

               The ratings are based, in varying degrees, on the following
    considerations: 

                    I. Likelihood of default-capacity and willingness of the
    obligor as to the timely payment of interest and repayment of principal in
    accordance with the terms of the obligation. 

                   II. Nature of and provisions of the obligation. 

                  III. Protection afforded by, and relative position of, the
    obligation in the event of bankruptcy, reorganization or other arrangement
    under the laws of bankruptcy and other laws affecting creditors' rights.

               AAA --  This is the highest rating assigned by Standard &
    Poor's to a debt obligation and indicates an extremely strong capacity to
    pay principal and interest. 

               AA --  Bonds rated AA also qualify as high-quality debt
    obligations.  Capacity to pay principal and interest is very strong, and
    they differ from AAA issues only in small degrees. 

               A --  Bonds rated A have a strong capacity to pay principal and
    interest, although they are somewhat more susceptible to the adverse
    effects of changes in circumstances and economic conditions. 

               BBB --  Bonds rated BBB are regarded as having an adequate
    capacity to pay principal and interest.  Whereas they normally exhibit
    adequate protection parameters, adverse economic conditions or changing
    circumstances are more likely to lead to a weakened capacity to pay
    principal and interest for bonds in this category than for bonds in the A
    category. 

               Plus (+) or Minus (-):  To provide more detailed indications of
    credit quality, the ratings from "AA" to "BB" may be modified by the
    addition of a plus or minus sign to show relative standing within the
    major rating categories. 

               Provisional Ratings (Prov.) following a rating indicates the
    rating is provisional, which assumes the successful completion of the
    project being financed by the issuance of the bonds being rated and
    indicates that payment of debt service requirements is largely or entirely
    dependent upon the successful and timely completion of the project.  This
    rating, however, while addressing credit quality subsequent to completion,
    makes no comment on the likelihood of, or the risk of default upon failure
    of, such completion.  Accordingly, the investor should exercise his own
    judgment with respect to such likelihood and risk. 

    Moody's Investors Service, Inc.

               A brief description of the applicable Moody's Investors
    Service, Inc. rating symbols and their meanings are as follows: 

               Aaa --  Bonds which are rated Aaa are judged to be of the best
    quality.  They carry the smallest degree of investment risk and are
    generally referred to as "gilt edge".  Interest payments are protected by
    a large or by an exceptionally stable margin and principal is secure. 
    While the various protective elements are likely to change, such changes
    as can be visualized are most unlikely to impair the fundamentally strong
    position of such issues. 

               Aa --  Bonds which are rated Aa are judged to be of high
    quality by all standards.  Together with the Aaa group they comprise what
    are generally known as high grade bonds. They are rated lower than the
    best bonds because margins of protection may not be as large as in Aaa
    securities or fluctuation of protective elements may be of greater
    amplitude or there may be other elements present which make the long-term
    risks appear somewhat larger than in Aaa securities. 

               A --  Bonds which are rated A possess many favorable investment
    attributes and are to be considered as upper medium grade obligations. 
    Factors giving security to principal and interest are considered adequate
    but elements may be present which suggest a susceptibility to impairment
    sometime in the future. 

               Baa --  Bonds which are rated Baa are considered as medium
    grade obligations, i.e., they are neither highly protected nor poorly
    secured.  Interest payments and principal security appear adequate for the
    present but certain protective elements may be lacking or may be
    characteristically unreliable over any great length of time.  Such bonds
    lack outstanding investment characteristics and in fact have speculative
    characteristics as well.  The market value of the Baa-rated bonds is more
    sensitive to changes in economic circumstances.  Aside from occasional
    speculative factors and the aforementioned economic circumstances applying
    to some bonds of this Class, Baa market valuations move in parallel with
    Aaa, Aa and A obligations during periods of economic normalcy, except in
    instances of oversupply.

               Those bonds in the A and Baa group which Moody's believes
    possess the strongest investment attributes are designated by the symbol
    A 1 and Baa 1.  Other A bonds comprise the balance of the group.  These
    rankings (1) designate the bonds which offer the maximum in security
    within their quality group, (2) designate bonds which can be bought for
    possible upgrading in quality and (3) additionally afford the investor an
    opportunity to gauge more precisely the relative attractiveness of
    offerings in the marketplace. 

               Moody's applies numerical modifiers, 1, 2 and 3 in each generic
    rating classification from Aa through B in its corporate bond rating
    system.  The modifier 1 indicates that the security ranks in the higher
    end of its generic rating category; the modifier 2 indicates a mid-range
    ranking; and the modifier 3 indicates that the issue ranks in the lower
    end of its generic rating category. 

               Con-Bonds for which the security depends upon the completion of
    some act or the fulfillment of some condition are rated conditionally. 
    These are debt obligations secured by (a) earnings of projects under
    construction, (b) earnings of projects unseasoned in operating experience,
    (c) rentals which begin when facilities are completed, or (d) payments to
    which some other limiting condition attaches.  Rating denotes probable
    credit stature upon completion of construction or elimination of basis of
    condition. 

                              DESCRIPTION OF RATING*


               A Standard & Poor's Corporation's rating on the units of an
    investment trust (hereinafter referred to collectively as "units" and
    "fund") is a current assessment of creditworthiness with respect to the
    investments held by such fund.  This assessment takes into consideration
    the financial capacity of the issuers and of any guarantors, insurers,
    lessees, or mortgagors with respect to such investments.  The assessment,
    however, does not take into account the extent to which fund expenses or
    portfolio asset sales for less than the fund's purchase price will reduce
    payment to the unit holder of the interest and principal required to be
    paid on the portfolio assets.  In addition, the rating is not a
    recommendation to purchase, sell, or hold units, inasmuch as the rating
    does not comment as to market price of the units or suitability for a
    particular investor. 


    *     As described by Standard & Poor's Corporation.


    <PAGE>

               Funds rated "AAA" are composed exclusively of assets that are
    rated "AAA" by Standard & Poor's or have, in the opinion of Standard &
    Poor's, credit characteristics comparable to assets that are rated "AAA",
    or certain short-term investments.  Standard & Poor's defines its AAA
    rating for such assets as the highest rating assigned by Standard & Poor's
    to a debt obligation.  Capacity to pay interest and repay principal is
    very strong. 


    <PAGE>
                  FOR USE WITH INSURED MUNICIPAL SECURITIES TRUST
                        SERIES 1 - 4 (MULTIPLIER PORTFOLIO)
                    SERIES 1 - 2 AND 1ST - 8TH DISCOUNT SERIES  


    ==========================================================================


            AUTHORIZATION FOR INVESTMENT IN MUNICIPAL SECURITIES TRUST
                           -- DISCOUNT SERIES/SERIES --
                        TRP PLAN - TOTAL REINVESTMENT PLAN


    I hereby elect to participate in the TRP Plan and am the owner of _____
    units ___ Discount Series/Series __________.

    I hereby authorize The Bank of New York, Trustee to pay all semi-annual or
    annual distributions of interest and principal (if any) with respect to
    such units to The Bank of New York, as TRP Plan Agent, who shall
    immediately invest the distributions in units of the available series of
    Insured Municipal Securities Trust above or, if unavailable, of other
    available series of Municipal Securities Trust. 


    The foregoing authorization is subject in        Date ______________, 19__
    all respects to the terms and conditions of
    participation set forth in the prospectus
    relating to such available series. 


    ___________________________________________                               
    Registered Holder (Print)                    Registered Holder (Print)


    ___________________________________________                               
    Registered Holder Signature                  Registered Holder Signature
                                           (Two signatures if joint tenancy)


    My Brokerage Firm's Name                                                  

    Street Address                                                            

    City, State and Zip Code                                                  

    Salesman's Name ___________________________  Salesman's No.               


                 UNIT HOLDERS NEED ONLY SIGN AND DATE THIS FORM. 


    ==========================================================================


                                MAIL TO YOUR BROKER
                                        OR
                               THE BANK OF NEW YORK


                       ATTN:  UNIT INVESTMENT TRUST DIVISION
                                101 BARCLAY STREET
                             NEW YORK, NEW YORK  10286


    <PAGE>
                  FOR USE WITH INSURED MUNICIPAL SECURITIES TRUST
                            9TH - 46TH DISCOUNT SERIES
                                   SERIES 3 - 19


    ==========================================================================


        AUTHORIZATION FOR INVESTMENT IN INSURED MUNICIPAL SECURITIES TRUST
                           -- DISCOUNT SERIES/SERIES --
                        TRP PLAN - TOTAL REINVESTMENT PLAN


    I hereby elect to participate in the TRP Plan and am the owner of _____
    units ___ Discount Series/Series _______.

    I hereby authorize the United States Trust Company of New York, Trustee,
    to pay all semi-annual or annual distributions of interest and principal
    (if any) with respect to such units to the United States Trust Company of
    New York, as TRP Plan Agent, who shall immediately invest the
    distributions in units of the available series of Insured Municipal
    Securities Trust above or, if unavailable, of other available series of
    Municipal Securities Trust. 


    The foregoing authorization is subject in        Date ______________, 19__
    all respects to the terms and conditions of
    participation set forth in the prospectus
    relating to such available series. 


    ___________________________________________                               
    Registered Holder (Print)                    Registered Holder (Print)


    ___________________________________________                               
    Registered Holder Signature                  Registered Holder Signature
                                           (Two signatures if joint tenancy)



    My Brokerage Firm's Name                                                  

    Street Address                                                            

    City, State and Zip Code                                                  

    Salesman's Name ___________________________  Salesman's No.               


                 UNIT HOLDERS NEED ONLY SIGN AND DATE THIS FORM. 


    ==========================================================================


                                MAIL TO YOUR BROKER
                                        OR
                     UNITED STATES TRUST COMPANY OF NEW YORK 
                     ATTN:  UNIT INVESTMENT DEPARTMENT, UNIT A
                                   770 BROADWAY
                             NEW YORK, NEW YORK  10003


    <PAGE>

     
                         INDEX                                INSURED
                                                     MUNICIPAL SECURITIES TRUST
     Title                                   Page     (Unit Investment Trust)
                                                             Prospectus
     Summary of Essential Information  . . .  A-5
     Information Regarding the Trust . . . .  A-7      Dated:  April 29, 1994
     Financial and Statistical Information .  A-8
     Audit and Financial Information                          Sponsor:
       Report of Independent Accountants . .  F-1    Bear, Stearns & Co. Inc. 
       Statement of Net Assets . . . . . . .  F-2         245 Park Avenue
       Statement of Operations . . . . . . .  F-3    New York, New York  10167
       Statement of Changes in Net Assets  .  F-4           212-272-2500
       Notes to Financial Statements . . . .  F-5
       Portfolio . . . . . . . . . . . . . .  F-6
     The Trust . . . . . . . . . . . . . . .    1
     Public Offering . . . . . . . . . . . .   12
     Estimated Long Term Return and                           Trustee:
       Estimated Current Return  . . . . . .   14
     Rights of Certificateholders  . . . . .   14   United States Trust Company
     Tax Status  . . . . . . . . . . . . . .   17           of New York
     Liquidity . . . . . . . . . . . . . . .   20           770 Broadway
     Total Reinvestment Plan . . . . . . . .   23    New York, New York  10003
     Trust Administration  . . . . . . . . .   27          1-800-428-8890
     Trust Expenses and Charges  . . . . . .   30
     Exchange Privilege and Conversion Offer   32                or
     Other Matters . . . . . . . . . . . . .   36
     Description of Bond Ratings . . . . . .   36      The Bank of New York 
     Description of Rating . . . . . . . . .   38        101 Barclay Street
                                                     New York, New York  10286
                                                           1-800-431-8002
     Parts A and B of this Prospectus do not
     contain all of the information set forth in
     the registration statement and exhibits
     relating thereto, filed with the Securities
     and Exchange Commission, Washington, D.C.,              Evaluator:
     under the Securities Act of 1933, and to
     which reference is made.                           Kenny S&P Evaluation
                                                              Services
                       *   *   *                            65 Broadway
                                                     New York, New York  10006 


               This Prospectus does not constitute an offer to sell, or a
    solicitation of an offer to buy, securities in any state to any person to
    whom it is not lawful to make such offer in such state. 

                                     *   *   *

               No person is authorized to give any information or to make any
    representations not contained in Parts A and B of this Prospectus; and any
    information or representation not contained herein must not be relied upon
    as having been authorized by the Trust, the Trustee, the Evaluator, or the
    Sponsor.  The Trust is registered as a unit investment trust under the
    Investment Company Act of 1940.  Such registration does not imply that the
    Trust or any of its Units have been guaranteed, sponsored, recommended or
    approved by the United States or any state or any agency or officer
    thereof.



    <PAGE>
                                      PART II

                        ADDITIONAL INFORMATION NOT REQUIRED
                                   IN PROSPECTUS

                        CONTENTS OF REGISTRATION STATEMENT


    This Post-Effective Amendment to the Registration Statement on Form S-6
    comprises the following papers and documents: 

    The facing sheet on Form S-6. 
    The Cross-Reference Sheet.
    The Prospectus consisting of     pages. 
    Signatures. 
    Consent of Independent Auditors.
    Consent of Counsel (included in Exhibits 99.3.1 and 99.3.1.1).
    Consents of the Evaluator and Confirmation of Ratings
      (included in Exhibit 99.5.1).

    The following exhibits: 

    99.1.1   --    Form of Reference Trust Agreement, as amended (filed as
                   Exhibit 1.1 to Amendment No. 1 to Form S-6 Registration
                   Statements Nos. 33-02389, 33-03180, 33-04508, 33-05571 and
                   33-06441 of Insured Municipal Securities Trust, 17th
                   Discount Series & Series 6, 18th Discount Series, 19th
                   Discount Series & Series 7, 20th Discount Series and 21st
                   Discount Series, respectively, on January 30, 1986,
                   March 26, 1986, April 24, 1986, May 29, 1986 and June 25,
                   1986, respectively, and incorporated herein by reference). 

    99.1.1.1 --    Trust Indenture and Agreement for Insured Municipal
                   Securities Trust, 9th Discount Series (and Subsequent
                   Series) (filed as Exhibit 1.1.1 to Amendment No. 1 to
                   Form S-6 Registration Statement No. 2-95854 of Insured
                   Municipal Securities Trust, 9th Discount Series on
                   April 11, 1985 and incorporated herein by reference). 
       
    99.1.3.4 --    Certificate of Incorporation of Bear, Stearns & Co. Inc.,
                   as amended (filed as Exhibit 99.1.3.4 to Form S-6
                   Registration Statement Nos. 33-50891 and 33-50901 of
                   Insured Municipal Securities Trust, New York Navigator
                   Insured Series 15 and New Jersey Navigator Insured Series
                   11; and Municipal Securities Trust, Multi-State Series 44,
                   respectively, on December 9, 1993 and incorporated herein
                   by reference). 
        
       
    99.1.3.5 --    By-Laws of Bear, Stearns & Co. Inc., as amended (filed as
                   Exhibit 99.1.3.5 to Form S-6 Registration Statement Nos.
                   33-50891 and 33-50901 of Insured Municipal Securities
                   Trust, New York Navigator Insured Series 15 and New Jersey
                   Navigator Insured Series 11; and Municipal Securities
                   Trust, Multi-State Series 44, respectively, on December 9,
                   1993 and incorporated herein by reference).
        
    99.1.4   --    Form of Agreement Among Underwriters (filed as Exhibit 1.4
                   to Amendment No. 1 to Form S-6 Registration Statement
                   No. 2-97191 of Insured Municipal Securities Trust, 10th
                   Discount Series and Series 3 on May 8, 1985 and
                   incorporated herein by reference).

    99.1.5   --    Form of Insurance Policy of Financial Guaranty Insurance
                   Company for Sponsor-Insured Bonds (filed as Exhibit 1.5 to
                   Amendment No. 1 to Form S-6 Registration Statement
                   No. 2-95261 of Insured Municipal Securities Trust, 7th
                   Discount Series on February 19, 1985 and incorporated
                   herein by reference).

    99.2.1   --    Form of Certificate (filed as Exhibit 2.1 to Amendment
                   No. 1 to Form S-6 Registration Statement No. 33-01313 of
                   Insured Municipal Securities Trust, 16th Discount Series on
                   November 27, 1985 and incorporated herein by reference). 

    99.3.1     --  Opinion of Battle Fowler (formerly Battle, Fowler, Jaffin &
                   Kheel) as to the legality of the securities being
                   registered, including their consent to the delivery thereof
                   and to the use of their name under the headings "Tax
                   Status" and "Legal Opinions" in the Prospectus, and to the
                   delivery of their opinion regarding tax status of the Trust
                   (filed as Exhibit 3.1 to Amendment No. 1 to Form S-6
                   Registration Statements Nos. 33-02389, 33-03180, 33-04508,
                   33-05571 and 33-06441 of Insured Municipal Securities
                   Trust, 17th Discount Series & Series 6, 18th Discount
                   Series, 19th Discount Series & Series 7, 20th Discount
                   Series and 21st Discount Series, respectively, on
                   January 30, 1986, March 26, 1986, April 24, 1986, May 29,
                   1986 and June 25, 1986, respectively, and incorporated
                   herein by reference). 

    99.3.1.1 --    Opinion of Battle Fowler (formerly Battle, Fowler, Jaffin &
                   Kheel) as to tax status of securities being registered
                   (filed as Exhibit 3.1.1 to Amendment No. 1 to Form S-6
                   Registration Statements Nos. 33-02389 of Insured Municipal
                   Securities Trust, 17th Discount Series & Series 6 on
                   January 30, 1986, and incorporated herein by reference). 

    
   *99.5.1   --    Consents of the Evaluator and Confirmation of Ratings by
                   Standard & Poor's Corporation.

    99.6.0   --    Power of Attorney of Bear, Stearns & Co. Inc., the
                   Depositor, by its Officers and a majority of its Directors
                   (filed as Exhibit 6.0 to Post-Effective Amendment No. 8 to
                   Form S-6 Registration Statements Nos. 2-92113, 2-92660,
                   2-93073, 2-93884 and 2-94545 of Municipal Securities Trust,
                   Multi-State Series 4, 5, 6, 7 and 8, respectively, on
                   October 30, 1992 and incorporated herein by reference).
    *     Being filed by this Amendment.


    <PAGE>
                          CONSENT OF INDEPENDENT AUDITORS

We consent to the use in these Post-Effective Amendments to the Registration 
Statements of our reports on the financial statements of Insured Municipal 
Securities Trust, 17th Discount Series; Insured Municipal Securities Trust, 
Series 6; Insured Municipal Securities Trust, 18th Discount Series; Insured 
Municipal Securities Trust, 19th Discount Series; Insured Municipal Securities 
Trust, Series 7; Insured Municipal Securities Trust, 20th Discount Series and 
Insured Municipal Securities Trust, 21st Discount Series included herein and 
to the reference to our firm under the heading "Independent Auditors" in the 
Prospectus which is part of this Registration Statement.




    
    KPMG PEAT MARWICK


New York, New York
April 15, 1994

    <PAGE>
                                    SIGNATURES

       
              Pursuant to the requirements of the Securities Act of 1933, the
    registrants, Insured Municipal Securities Trust, 17th Discount Series &
    Series 6, 18th Discount Series, 19th Discount Series & Series 7, 20th
    Discount Series and 21st Discount Series certify that they have met all of
    the requirements for effectiveness of this Post-Effective Amendment to the
    Registration Statements pursuant to Rule 485(b) under the Securities Act
    of 1933.  The registrants have duly caused this Post-Effective Amendment
    to the Registration Statements to be signed on their behalf by the
    undersigned, thereunto duly authorized, in the City of New York and State
    of New York on the 20th day of April, 1994.
        
                   INSURED MUNICIPAL SECURITIES TRUST,
                   17TH DISCOUNT SERIES & SERIES 6, 18TH DISCOUNT SERIES,
                   19TH DISCOUNT SERIES & SERIES 7, 20TH DISCOUNT SERIES
                   and 21ST DISCOUNT SERIES
                        (Registrants)

                   BEAR, STEARNS & CO. INC.
                        (Depositor)


                   By:  PETER J. DeMARCO           
                        (Authorized Signator)

              Pursuant to the requirements of the Securities Act of 1933, this
    Post-Effective Amendment to the Registration Statements has been signed
    below by the following persons who constitute the principal officers and a
    majority of the directors of Bear, Stearns & Co. Inc., the Depositor, in
    the capacities and on the dates indicated.

       
    Name                  Title                              Date

    ALAN C. GREENBERG     Chairman of the Board, Chief      )
                          Executive Officer, Director and   )
                          Senior Managing Director          )
    JAMES E. CAYNE        President, Director and Senior    )April 20, 1994
                          Managing Director                 )
    ALVIN H. EINBENDER    Chief Operating Officer, Executive)
                          Vice President, Director and      )
                          Senior Managing Director          )
    JOHN C. SITES, JR.    Executive Vice President, Director)By:PETER J. DeMARCO
                          and Senior Managing Director      ) Attorney-in-Fact*
    MICHAEL L. TARNOPOL   Executive Vice President, Director)
                          and Senior Managing Director      )
    VINCENT J. MATTONE    Executive Vice President, Director)
                          and Senior Managing Director      )
    ALAN D. SCHWARTZ      Executive Vice President, Director)
                          and Senior Managing Director      )
    DOUGLAS P.C. NATION   Director and Senior Managing      )
                          Director                          )
    WILLIAM J. MONTGORIS  Chief Financial Officer, Senior   )
                          Vice President-Finance and Senior )
                          Managing Director                 )
    KENNETH L. EDLOW      Secretary and Senior Managing     )
                          Director                          )
    MICHAEL MINIKES       Treasurer and Senior Managing     )
                          Director                          )
    MICHAEL J. ABATEMARCO Controller, Assistant Secretary   )
                          and Senior Managing Director      )
    MARK E. LEHMAN        Senior Vice President - General   )
                          Counsel and Senior Managing       )
                          Director                          )
    FREDERICK B. CASEY    Assistant Treasurer and Senior    )
                          Managing Director                 )
        
    _______________

    *    An executed power of attorney was filed as Exhibit 6.0 to Post-
         Effective Amendment No. 8 to Registration Statements Nos. 2-92113,
         2-92660, 2-93073, 2-93884 and 2-94545 on October 30, 1992.

    <PAGE>
                                   EXHIBIT INDEX


    Exhibit        Description                                        Page No.

    99.1.1         Form of Reference Trust Agreement, as
                   amended (filed as Exhibit 1.1 to Amendment
                   No. 1 to Form S-6 Registration Statements
                   Nos. 33-02389, 33-03180, 33-04508, 33-05571
                   and 33-06441 of Insured Municipal Securities
                   Trust, 17th Discount Series & Series 6, 18th
                   Discount Series, 19th Discount Series &
                   Series 7, 20th Discount Series and 21st
                   Discount Series, respectively, on
                   January 30, 1986, March 26, 1986, April 24,
                   1986, May 29, 1986 and June 25, 1986,
                   respectively, and incorporated herein by
                   reference). 

    99.1.1.1       Trust Indenture and Agreement for Insured
                   Municipal Securities Trust, 9th Discount Series
                   (and Subsequent Series) (filed as Exhibit 1.1.1
                   to Amendment No. 1 to Form S-6 Registration
                   Statement No. 2-95854 of Insured Municipal
                   Securities Trust, 9th Discount Series on
                   April 11, 1985 and incorporated herein by
                   reference). 
       
    99.1.3.4       Certificate of Incorporation of Bear, Stearns &
                   Co. Inc., as amended (filed as Exhibit 99.1.3.4
                   to Form S-6 Registration Statement Nos. 33-50891
                   and 33-50901 of Insured Municipal Securities
                   Trust, New York Navigator Insured Series 15 and
                   New Jersey Navigator Insured Series 11; and
                   Municipal Securities Trust, Multi-State Series
                   44, respectively, on December 9, 1993 and
                   incorporated herein by reference).
        
       
    99.1.3.5       By-Laws of Bear, Stearns & Co. Inc., as amended
                   (filed as Exhibit 99.1.3.5 to Form S-6
                   Registration Statement Nos. 33-50891 and 33-50901
                   of Insured Municipal Securities Trust, New York
                   Navigator Insured Series 15 and New Jersey
                   Navigator Insured Series 11; and Municipal
                   Securities Trust, Multi-State Series 44,
                   respectively, on December 9, 1993 and
                   incorporated herein by reference).
        
    99.1.4         Form of Agreement Among Underwriters (filed as
                   Exhibit 1.4 to Amendment No. 1 to Form S-6
                   Registration Statement No. 2-97191 of Insured
                   Municipal Securities Trust, 10th Discount Series
                   and Series 3 on May 8, 1985 and incorporated
                   herein by reference).

    99.1.5         Form of Insurance Policy of Financial
                   Guaranty Insurance Company for Sponsor-
                   Insured Bonds (filed as Exhibit 1.5 to
                   Amendment No. 1 to Form S-6 Registration
                   Statement No. 2-95261 of Insured Municipal
                   Securities Trust, 7th Discount Series on
                   February 19, 1985 and incorporated herein by
                   reference).

    99.2.1         Form of Certificate (filed as Exhibit 2.1 to
                   Amendment No. 1 to Form S-6 Registration
                   Statement No. 33-01313 of Insured Municipal
                   Securities Trust, 16th Discount Series on
                   November 27, 1985 and incorporated herein by
                   reference). 

    99.3.1         Opinion of Battle Fowler (formerly Battle,
                   Fowler, Jaffin & Kheel) as to the legality
                   of the securities being registered,
                   including their consent to the delivery
                   thereof and to the use of their name under
                   the headings "Tax Status" and "Legal
                   Opinions" in the Prospectus, and to the
                   delivery of their opinion regarding tax
                   status of the Trust (filed as Exhibit 3.1 to
                   Amendment No. 1 to Form S-6 Registration
                   Statements Nos. 33-02389, 33-03180,
                   33-04508, 33-05571 and 33-06441 of Insured
                   Municipal Securities Trust, 17th Discount
                   Series & Series 6, 18th Discount Series,
                   19th Discount Series & Series 7, 20th
                   Discount Series and 21st Discount Series,
                   respectively, on January 30, 1986, March 26,
                   1986, April 24, 1986, May 29, 1986 and
                   June 25, 1986, respectively, and
                   incorporated herein by reference). 

    99.3.1.1       Opinion of Battle Fowler (formerly Battle,
                   Fowler, Jaffin & Kheel) as to tax status of
                   securities being registered (filed as
                   Exhibit 3.1.1 to Amendment No. 1 to Form S-6
                   Registration Statements Nos. 33-02389 of Insured
                   Municipal Securities Trust, 17th Discount Series
                   & Series 6 on January 30, 1986, and incorporated
                   herein by reference). 

    99.5.1         Consents of the Evaluator and Confirmation of
                   Ratings by Standard & Poor's Corporation.........

    99.6.0         Power of Attorney of Bear, Stearns & Co.
                   Inc., the Depositor, by its Officers and a
                   majority of its Directors (filed as
                   Exhibit 6.0 to Post-Effective Amendment
                   No. 8 to Form S-6 Registration Statements
                   Nos. 2-92113, 2-92660, 2-93073, 2-93884 and
                   2-94545 of Municipal Securities Trust,
                   Multi-State Series 4, 5, 6, 7 and 8,
                   respectively, on October 30, 1992 and
                   incorporated herein by reference).



                           KENNY S&P EVALUATION SERVICES
                   A Division of Kenny Information Systems, Inc.

                                    65 Broadway
                           New York, New York 10006-2511
                              Telephone 212/770-4990

                                    F.A. Shinal
                               Senior Vice President
                              Chief Financial Officer

       
                             April 29, 1994
        

    Bear, Stearns & Co., Inc.
    245 Park Avenue
    New York, NY 10167

              RE:  Insured Municipal Securities Trust
                   17th Discount Series and Series 6

    Gentlemen:

              We have examined the post-effective Amendment to the
    Registration Statement File No. 33-02389 for the above-captioned trust. 
    We hereby acknowledge that Kenny S&P Evaluation Services, a division of
    Kenny Information Systems, Inc. is currently acting as the evaluator for
    the trust.  We hereby consent to the use in the Amendment of the reference
    to Kenny S&P Evaluation Services, a division of Kenny Information Systems,
    Inc. as evaluator.

              In addition, we hereby confirm that the ratings indicated in the
    above-referenced Amendment to the Registration Statement for the
    respective bonds comprising the trust portfolio  are the ratings currently
    indicated in our KENNYBASE database.  

              You are hereby authorized to file a copy of this letter with the
    Securities and Exchange Commission.

                                  Sincerely,



                                  F. A. Shinal
                                  Senior Vice President

    FAS/cns
<PAGE>

    Standard & Poor's Corporation
    Bond Insurance Administration
    25 Broadway
    New York, New York 10004-1064
    Telephone 212/208-1740
    FAX 212/208-8262

                                            April 29, 1994

    Bear Stearns & Co., Inc.
    245 Park Avenue
    New York, New York  10167

    Re:  Insured Municipal Securities Trust, 17th Discount Series and Series 6

         We have received the post-effective amendment to the registration
    statement SEC file number 33-02389 for the above captioned trust.

         Since the portfolio is composed solely of securities covered by bond
    insurance policies that insure against default in the payment of principal
    and interest on the securities for so long as they remain outstanding and
    such policies have been issued by one or more insurance companies which
    have been assigned 'AA' or better claims paying ability rating by S&P, we
    assign a 'AA-' rating to the units of the trust.

         You have permission to use the name of Standard & Poor's Corporation
    and the above-assigned rating in connection with your dissemination of
    information relating to these units, provided, however, that this letter
    does not constitute S&P's consent to you using the name Standard & Poor's
    Corporation or the above-assigned rating in any prospectus or registration
    statement relating to the units or the trust.  You understand that S&P has
    not consented to, and will not consent to, being named as an "expert"
    under the federal securities laws, including, without limitation, Section
    7 of the Securities Act of 1933.  In addition, it should be understood
    that the rating is not a "market" rating nor a recommendation to buy,
    hold, or sell the units of the trust.  S&P reserves the right to advise
    its own clients, subscribers, and the public of the rating.  Further, it
    should be undersood that the rating on the units does not take into
    account the extent to which fund expenses or portfolio asset sales for
    less than the fund's purchase price will reduce payment to the unit
    holders of the interest and principal required to be paid on the portfolio
    assets.  S&P relies on the sponsor and its counsel, accountants, and other
    experts for the accuracy and completeness of the information submitted in
    connection with the ratings.  S&P does not independently verify the truth
    or accuracy of any such information.

         We are pleased to have had the opportunity to be of service to you. 
    If we can be of further help, please do not hesitate to call upon us.

                                            Sincerely,


                                            Vincent S. Orgo
    /mc

    <PAGE>
                           KENNY S&P EVALUATION SERVICES
                   A Division of Kenny Information Systems, Inc.

                                    65 Broadway
                           New York, New York 10006-2511
                              Telephone 212/770-4990

                                    F.A. Shinal
                               Senior Vice President
                              Chief Financial Officer

       
                             April 29, 1994
        


    Bear, Stearns & Co., Inc.
    245 Park Avenue
    New York, NY 10167

              RE:  Insured Municipal Securities Trust
                   18th Discount Series        

    Gentlemen:

              We have examined the post-effective Amendment to the
    Registration Statement File No. 33-03180 for the above-captioned trust. 
    We hereby acknowledge that Kenny S&P Evaluation Services, a division of
    Kenny Information Systems, Inc. is currently acting as the evaluator for
    the trust.  We hereby consent to the use in the Amendment of the reference
    to Kenny S&P Evaluation Services, a division of Kenny Information Systems,
    Inc. as evaluator.

              In addition, we hereby confirm that the ratings indicated in the
    above-referenced Amendment to the Registration Statement for the
    respective bonds comprising the trust portfolio  are the ratings currently
    indicated in our KENNYBASE database.  

              You are hereby authorized to file a copy of this letter with the
    Securities and Exchange Commission.

                                  Sincerely,



                                  F. A. Shinal
                                  Senior Vice President

    FAS/cns
<PAGE>

    Standard & Poor's Corporation
    Bond Insurance Administration
    25 Broadway
    New York, New York 10004-1064
    Telephone 212/208-1740
    FAX 212/208-8262

                                            April 29, 1994

    Bear Stearns & Co., Inc.
    245 Park Avenue
    New York, New York  10167

    Re:  Insured Municipal Securities Trust, 18th Discount Series

         We have received the post-effective amendment to the registration
    statement SEC file number 33-03180 for the above captioned trust.

         Since the portfolio is composed solely of securities covered by bond
    insurance policies that insure against default in the payment of principal
    and interest on the securities for so long as they remain outstanding and
    such policies have been issued by one or more insurance companies which
    have been assigned 'AAA' claims paying ability ratings by S&P, we reaffirm
    the assignment of a 'AAA' rating to the units of the trust and a 'AAA'
    rating to the securities contained in the trust.

         You have permission to use the name of Standard & Poor's Corporation
    and the above-assigned ratings in connection with your dissemination of
    information relating to these units, provided that it is understood that
    the ratings are not "market" ratings nor recommendations to buy, hold, or
    sell the units of the trust or the securities in the trust.  Further, it
    should be understood that the rating on the units does not take into
    account the extent to which fund expenses or portfolio asset sales for
    less than the fund's purchase price will reduce payment to the unit
    holders of the interest and principal required to be paid on the portfolio
    assets.  S&P reserves the right to advise its own clients, subscribers,
    and the public of the ratings.  S&P relies on the sponsor and its counsel,
    accountants, and other experts for the accuracy and completeness of the
    information submitted in connection with the ratings.  S&P does not
    independently verify the truth or accuracy of any such information.

         This letter evidences our consent to the use of the name of Standard
    & Poor's Corporation in connection with the rating assigned to the units
    in the amendment referred to above.  However, this letter should not be
    construed as a consent by us, within the meaning of Section 7 of the
    Securities Act of 1933, to the use of the name of Standard & Poor's
    Corporation in connection with the ratings assigned to the securities
    contained in the trust.  You are hereby authorized to file a copy this
    letter with the Securities and Exchange Commission.

         We are pleased to have had the opportunity to be of service to you. 
    If we can be of further help, please do not hesitate to call upon us.

                                            Sincerely,



                                            Vincent S. Orgo
    /mc

    <PAGE>
                           KENNY S&P EVALUATION SERVICES
                   A Division of Kenny Information Systems, Inc.

                                    65 Broadway
                           New York, New York 10006-2511
                              Telephone 212/770-4990

                                    F.A. Shinal
                               Senior Vice President
                              Chief Financial Officer


       
                             April 29, 1994
        

    Bear, Stearns & Co., Inc.
    245 Park Avenue
    New York, NY 10167

              RE:  Insured Municipal Securities Trust
                   19th Discount Series and Series 7 

    Gentlemen:

              We have examined the post-effective Amendment to the
    Registration Statement File No. 33-04508 for the above-captioned trust. 
    We hereby acknowledge that Kenny S&P Evaluation Services, a division of
    Kenny Information Systems, Inc. is currently acting as the evaluator for
    the trust.  We hereby consent to the use in the Amendment of the reference
    to Kenny S&P Evaluation Services, a division of Kenny Information Systems,
    Inc. as evaluator.

              In addition, we hereby confirm that the ratings indicated in the
    above-referenced Amendment to the Registration Statement for the
    respective bonds comprising the trust portfolio  are the ratings currently
    indicated in our KENNYBASE database.  

              You are hereby authorized to file a copy of this letter with the
    Securities and Exchange Commission.

                                  Sincerely,



                                  F. A. Shinal 
                                  Senior Vice President
    FAS/cns
<PAGE>
    Standard & Poor's Corporation
    Bond Insurance Administration
    25 Broadway
    New York, New York 10004-1064
    Telephone 212/208-1740
    FAX 212/208-8262

                                            April 29, 1994

    Bear Stearns & Co., Inc.
    245 Park Avenue
    New York, New York  10167

    Re:  Insured Municipal Securities Trust, 19th Discount Series and Series 7

         We have received the post-effective amendment to the registration
    statement SEC file number 33-04508 for the above captioned trust.

         Since the portfolio is composed solely of securities covered by bond
    insurance policies that insure against default in the payment of principal
    and interest on the securities for so long as they remain outstanding and
    such policies have been issued by one or more insurance companies which
    have been assigned 'AAA' claims paying ability ratings by S&P, we reaffirm
    the assignment of a 'AAA' rating to the units of the trust and a 'AAA'
    rating to the securities contained in the trust.

         You have permission to use the name of Standard & Poor's Corporation
    and the above-assigned ratings in connection with your dissemination of
    information relating to these units, provided that it is understood that
    the ratings are not "market" ratings nor recommendations to buy, hold, or
    sell the units of the trust or the securities in the trust.  Further, it
    should be understood that the rating on the units does not take into
    account the extent to which fund expenses or portfolio asset sales for
    less than the fund's purchase price will reduce payment to the unit
    holders of the interest and principal required to be paid on the portfolio
    assets.  S&P reserves the right to advise its own clients, subscribers,
    and the public of the ratings.  S&P relies on the sponsor and its counsel,
    accountants, and other experts for the accuracy and completeness of the
    information submitted in connection with the ratings.  S&P does not
    independently verify the truth or accuracy of any such information.

         This letter evidences our consent to the use of the name of Standard
    & Poor's Corporation in connection with the rating assigned to the units
    in the amendment referred to above.  However, this letter should not be
    construed as a consent by us, within the meaning of Section 7 of the
    Securities Act of 1933, to the use of the name of Standard & Poor's
    Corporation in connection with the ratings assigned to the securities
    contained in the trust.  You are hereby authorized to file a copy this
    letter with the Securities and Exchange Commission.

         We are pleased to have had the opportunity to be of service to you. 
    If we can be of further help, please do not hesitate to call upon us.

                                            Sincerely,


                                            Vincent S. Orgo
    /mc


    <PAGE>

                           KENNY S&P EVALUATION SERVICES
                   A Division of Kenny Information Systems, Inc.
                                    65 Broadway
                           New York, New York 10006-2511
                              Telephone 212/770-4990

                                    F.A. Shinal
                               Senior Vice President
                              Chief Financial Officer

       
                             April 29, 1994
        

    Bear, Stearns & Co., Inc.
    245 Park Avenue
    New York, NY 10167

              RE:  Insured Municipal Securities Trust
                   20th Discount Series    

    Gentlemen:

              We have examined the post-effective Amendment to the
    Registration Statement File No. 33-05571 for the above-captioned trust. 
    We hereby acknowledge that Kenny S&P Evaluation Services, a division of
    Kenny Information Systems, Inc. is currently acting as the evaluator for
    the trust.  We hereby consent to the use in the Amendment of the reference
    to Kenny S&P Evaluation Services, a division of Kenny Information Systems,
    Inc. as evaluator.

              In addition, we hereby confirm that the ratings indicated in the
    above-referenced Amendment to the Registration Statement for the
    respective bonds comprising the trust portfolio  are the ratings currently
    indicated in our KENNYBASE database.  

              You are hereby authorized to file a copy of this letter with the
    Securities and Exchange Commission.

                                  Sincerely,



                                  F. A. Shinal 
                                  Senior Vice President

    FAS/cns
<PAGE>

    Standard & Poor's Corporation
    Bond Insurance Administration
    25 Broadway
    New York, New York 10004-1064
    Telephone 212/208-1740
    FAX 212/208-8262
                                           April 29, 1994

    Bear Stearns & Co., Inc.
    245 Park Avenue
    New York, New York  10167

    Re:  Insured Municipal Securities Trust, 20th Discount Series

         We have received the post-effective amendment to the registration
    statement SEC file number 33-05571 for the above captioned trust.

         Since the portfolio is composed solely of securities covered by bond
    insurance policies that insure against default in the payment of principal
    and interest on the securities for so long as they remain outstanding and
    such policies have been issued by one or more insurance companies which
    have been assigned 'AAA' claims paying ability ratings by S&P, we reaffirm
    the assignment of a 'AAA' rating to the units of the trust and a 'AAA'
    rating to the securities contained in the trust.

         You have permission to use the name of Standard & Poor's Corporation
    and the above-assigned ratings in connection with your dissemination of
    information relating to these units, provided that it is understood that
    the ratings are not "market" ratings nor recommendations to buy, hold, or
    sell the units of the trust or the securities in the trust.  Further, it
    should be understood that the rating on the units does not take into
    account the extent to which fund expenses or portfolio asset sales for
    less than the fund's purchase price will reduce payment to the unit
    holders of the interest and principal required to be paid on the portfolio
    assets.  S&P reserves the right to advise its own clients, subscribers,
    and the public of the ratings.  S&P relies on the sponsor and its counsel,
    accountants, and other experts for the accuracy and completeness of the
    information submitted in connection with the ratings.  S&P does not
    independently verify the truth or accuracy of any such information.

         This letter evidences our consent to the use of the name of Standard
    & Poor's Corporation in connection with the rating assigned to the units
    in the amendment referred to above.  However, this letter should not be
    construed as a consent by us, within the meaning of Section 7 of the
    Securities Act of 1933, to the use of the name of Standard & Poor's
    Corporation in connection with the ratings assigned to the securities
    contained in the trust.  You are hereby authorized to file a copy this
    letter with the Securities and Exchange Commission.

         We are pleased to have had the opportunity to be of service to you. 
    If we can be of further help, please do not hesitate to call upon us.

                                            Sincerely,



                                            Vincent S. Orgo
    /mc
    <PAGE>

                           KENNY S&P EVALUATION SERVICES
                   A Division of Kenny Information Systems, Inc.

                                    65 Broadway
                           New York, New York 10006-2511
                              Telephone 212/770-4990

                                    F.A. Shinal
                               Senior Vice President
                              Chief Financial Officer


       
                             April 29, 1994
        

    Bear, Stearns & Co., Inc.
    245 Park Avenue
    New York, NY 10167

              RE:  Insured Municipal Securities Trust
                   21st Discount Series        

    Gentlemen:

              We have examined the post-effective Amendment to the
    Registration Statement File No. 33-06441 for the above-captioned trust. 
    We hereby acknowledge that Kenny S&P Evaluation Services, a division of
    Kenny Information Systems, Inc. is currently acting as the evaluator for
    the trust.  We hereby consent to the use in the Amendment of the reference
    to Kenny S&P Evaluation Services, a division of Kenny Information Systems,
    Inc. as evaluator.

              In addition, we hereby confirm that the ratings indicated in the
    above-referenced Amendment to the Registration Statement for the
    respective bonds comprising the trust portfolio  are the ratings currently
    indicated in our KENNYBASE database.  

              You are hereby authorized to file a copy of this letter with the
    Securities and Exchange Commission.

                                  Sincerely,


                                  F. A. Shinal
                                  Senior Vice President

    FAS/cns
<PAGE>

    Standard & Poor's Corporation
    Bond Insurance Administration
    25 Broadway
    New York, New York 10004-1064
    Telephone 212/208-1740
    FAX 212/208-8262

                                            April 29, 1994

    Bear Stearns & Co., Inc.
    245 Park Avenue
    New York, New York  10167

    Re:  Insured Municipal Securities Trust, 21st Discount Series

         We have received the post-effective amendment to the registration
    statement SEC file number 33-06441 for the above captioned trust.

         Since the portfolio is composed solely of securities covered by bond
    insurance policies that insure against default in the payment of principal
    and interest on the securities for so long as they remain outstanding and
    such policies have been issued by one or more insurance companies which
    have been assigned 'AAA' claims paying ability ratings by S&P, we reaffirm
    the assignment of a 'AAA' rating to the units of the trust and a 'AAA'
    rating to the securities contained in the trust.

         You have permission to use the name of Standard & Poor's Corporation
    and the above-assigned ratings in connection with your dissemination of
    information relating to these units, provided that it is understood that
    the ratings are not "market" ratings nor recommendations to buy, hold, or
    sell the units of the trust or the securities in the trust.  Further, it
    should be understood that the rating on the units does not take into
    account the extent to which fund expenses or portfolio asset sales for
    less than the fund's purchase price will reduce payment to the unit
    holders of the interest and principal required to be paid on the portfolio
    assets.  S&P reserves the right to advise its own clients, subscribers,
    and the public of the ratings.  S&P relies on the sponsor and its counsel,
    accountants, and other experts for the accuracy and completeness of the
    information submitted in connection with the ratings.  S&P does not
    independently verify the truth or accuracy of any such information.

         This letter evidences our consent to the use of the name of Standard
    & Poor's Corporation in connection with the rating assigned to the units
    in the amendment referred to above.  However, this letter should not be
    construed as a consent by us, within the meaning of Section 7 of the
    Securities Act of 1933, to the use of the name of Standard & Poor's
    Corporation in connection with the ratings assigned to the securities
    contained in the trust.  You are hereby authorized to file a copy this
    letter with the Securities and Exchange Commission.

         We are pleased to have had the opportunity to be of service to you. 
    If we can be of further help, please do not hesitate to call upon us.

                                            Sincerely,



                                            Vincent S. Orgo
    /mc



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