DEFINED ASSET FUNDS MUNICIPAL INVT TR FD INSURED SERIES 186
485BPOS, 2000-03-08
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     AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON MARCH 8, 2000

                                                       REGISTRATION NO. 33-49159
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------

                       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:
                             DEFINED ASSET FUNDS--
                        MUNICIPAL INVESTMENT TRUST FUND
                              INSURED SERIES--186

B. NAME OF DEPOSITOR:

                   MERRILL LYNCH, PIERCE, FENNER & SMITH INC.
                           SALOMON SMITH BARNEY INC.
                       PRUDENTIAL SECURITIES INCORPORATED
                            PAINEWEBBER INCORPORATED
                           DEAN WITTER REYNOLDS INC.

C. COMPLETE ADDRESSES OF DEPOSITORS' PRINCIPAL EXECUTIVE OFFICES:

<TABLE>
<S>                        <C>                        <C>
 MERRILL LYNCH, PIERCE,
     FENNER & SMITH
      INCORPORATED
   DEFINED ASSET FUNDS
  POST OFFICE BOX 9051
PRINCETON, NJ 08543-9051                              SALOMON SMITH BARNEY INC.
                                                            388 GREENWICH
                                                         STREET--23RD FLOOR
                                                         NEW YORK, NY 10013
</TABLE>

<TABLE>
    <S>                          <C>                          <C>
      PRUDENTIAL SECURITIES      PAINEWEBBER INCORPORATED     DEAN WITTER REYNOLDS INC.
          INCORPORATED              1285 AVENUE OF THE             TWO WORLD TRADE
       ONE NEW YORK PLAZA                AMERICAS                CENTER--59TH FLOOR
       NEW YORK, NY 10292           NEW YORK, NY 10019           NEW YORK, NY 10048
</TABLE>

D. NAMES AND COMPLETE ADDRESSES OF AGENTS FOR SERVICE:

<TABLE>
<CAPTION>

<S>                        <C>                        <C>
  TERESA KONCICK, ESQ.         ROBERT E. HOLLEY           MICHAEL KOCHMANN
      P.O. BOX 9051            1200 HARBOR BLVD.        388 GREENWICH STREET
PRINCETON, NJ 08543-9051      WEEHAWKEN, NJ 07087        NEW YORK, NY 10013

                                  COPIES TO:             DOUGLAS LOWE, ESQ.
                            PIERRE DE SAINT PHALLE,   DEAN WITTER REYNOLDS INC.
   LEE B. SPENCER, JR.               ESQ.                  TWO WORLD TRADE
   ONE NEW YORK PLAZA        450 LEXINGTON AVENUE        CENTER--59TH FLOOR
   NEW YORK, NY 10292         NEW YORK, NY 10017         NEW YORK, NY 10048
</TABLE>

The issuer has registered an indefinite number of Units under the Securities Act
of 1933 pursuant to Rule 24f-2 and will file the Rule 24f-2 Notice for the most
recent fiscal year in March, 2000.

Check box if it is proposed that this filing will become effective on March 17,
2000 pursuant to paragraph (b) of Rule 485.  /X/

- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
<PAGE>
                           DEFINED ASSET FUNDS--REGISTERED TRADEMARK--
                           ----------------------------------------------------

                           MUNICIPAL INVESTMENT TRUST FUND
                           INSURED SERIES--186
                           (A UNIT INVESTMENT TRUST)
                           -  PORTFOLIO OF INSURED LONG TERM MUNICIPAL BONDS
                           -  DESIGNED TO BE FREE OF REGULAR FEDERAL INCOME TAX
                           -  MONTHLY INCOME DISTRIBUTIONS

SPONSORS:
MERRILL LYNCH,
PIERCE, FENNER & SMITH
INCORPORATED               -----------------------------------------------------
SALOMON SMITH BARNEY INC.  The Securities and Exchange Commission has not
PRUDENTIAL SECURITIES      approved or disapproved these Securities or passed
INCORPORATED               upon the adequacy of this prospectus. Any
PAINEWEBBER INCORPORATED   representation to the contrary is a criminal offense.
DEAN WITTER REYNOLDS INC.  Prospectus dated March 17, 2000.

<PAGE>
- --------------------------------------------------------------------------------

Defined Asset Funds--Registered Trademark--
Defined Asset Funds-Registered Trademark- is America's oldest and largest family
of unit investment trusts, with over $160 billion sponsored over the last 28
years. Defined Asset Funds has been a leader in unit investment trust research
and product innovation. Our family of Funds helps investors work toward their
financial goals with a full range of quality investments, including municipal,
corporate and government bond portfolios, as well as domestic and international
equity portfolios.

Defined Asset Funds offer a number of advantages:
  - A disciplined strategy of buying and holding with a long-term view is the
    cornerstone of Defined Asset Funds.
  - Fixed portfolio: Defined Funds follow a buy and hold investment strategy;
    funds are not managed and portfolio changes are limited.
  - Defined Portfolios: We choose the stocks and bonds in advance, so you know
    what you're investing in.
  - Professional research: Our dedicated research team seeks out stocks or bonds
    appropriate for a particular fund's objectives.
  - Ongoing supervision: We monitor each portfolio on an ongoing basis.
No matter what your investment goals, tolerance for risk or time horizon,
there's probably a Defined Asset Fund that suits your investment style. Your
financial professional can help you select a Defined Asset Fund that works best
for your investment portfolio.

THE FINANCIAL INFORMATION IN THIS PROSPECTUS IS AS OF THE EVALUATION DATE,
DECEMBER 31, 1999.

<TABLE>
<S>                                    <C>
CONTENTS
                                       PAGE
                                       ----
Risk/Return Summary..................     3
What You Can Expect From Your
  Investment.........................     7
  Monthly Income.....................     7
  Return Figures.....................     7
  Records and Reports................     7
The Risks You Face...................     8
  Interest Rate Risk.................     8
  Call Risk..........................     8
  Reduced Diversification Risk.......     8
  Liquidity Risk.....................     8
  Concentration Risk.................     8
  Bond Quality Risk..................     9
  Insurance Related Risk.............     9
  Litigation and Legislation Risks...     9
Selling or Exchanging Units..........     9
  Sponsors' Secondary Market.........     9
  Selling Units to the Trustee.......    10
  Exchange Option....................    10
How The Fund Works...................    11
  Pricing............................    11
  Evaluations........................    11
  Income.............................    11
  Expenses...........................    11
  Portfolio Changes..................    12
  Fund Termination...................    12
  Certificates.......................    12
  Trust Indenture....................    13
  Legal Opinion......................    13
  Auditors...........................    13
  Sponsors...........................    14
  Trustee............................    14
  Underwriters' and Sponsors'
    Profits..........................    14
  Public Distribution................    14
  Code of Ethics.....................    14
  Year 2000 Issues...................    15
Taxes................................    15
Supplemental Information.............    16
Financial Statements.................   D-1
</TABLE>

                                       2
<PAGE>
- --------------------------------------------------------------------------------

RISK/RETURN SUMMARY

<TABLE>
<C>  <S>
 1.  WHAT IS THE FUND'S OBJECTIVE?
     The Fund seeks interest income that is
     exempt from regular federal income taxes
     by investing in a fixed portfolio
     consisting primarily of insured
     municipal revenue bonds.

 2.  WHAT ARE MUNICIPAL REVENUE BONDS?
     Municipal revenue bonds are bonds issued
     by states, municipalities and public
     authorities to finance the cost of
     buying, building or improving various
     projects intended to generate revenue,
     such as airports, health care
     facilities, housing and municipal
     electric, water and sewer utilities.
     Generally, payments on these bonds
     depend solely on the revenues generated
     by the projects, excise taxes or state
     appropriations, and are not backed by
     the government's taxing power.

 3.  WHAT IS THE FUND'S INVESTMENT STRATEGY?

  -  The Fund plans to hold to maturity 12
     insured long-term tax-exempt municipal
     bonds with a current aggregate face
     amount of $9,735,000.

  -  The Fund is a unit investment trust
     which means that, unlike a mutual fund,
     the Fund's portfolio is not managed.
  -  The bonds are rated AAA or Aaa by
     Standard & Poor's, Moody's or Fitch.
  -  The Fund is concentrated in refunded
     bonds.
  -  Many of the bonds can be called at a
     premium declining over time to par
     value. Some bonds may be called earlier
     at par for extraordinary reasons.
  -  100% of the bonds are insured by
     insurance companies. Insurance
     guarantees timely payments of principal
     and interest on the bonds (but not Fund
     units or the market value of the bonds
     before they mature).

     The Portfolio consists of municipal
     bonds of the following types:
</TABLE>

<TABLE>
  -  Hospitals/Health Care                    31%
<C>  <S>
  -  Housing                                   6%
  -  Municipal Water/Sewer Utilities          10%
  -  Refunded Bonds                          28%
  -  Municipal Electric Utilities              6%
  -  Universities/Colleges                    19%
</TABLE>

<TABLE>
<C>  <S>
 4.  WHAT ARE THE SIGNIFICANT RISKS?

     YOU CAN LOSE MONEY BY INVESTING IN THE
     FUND. THIS CAN HAPPEN FOR VARIOUS
     REASONS, INCLUDING:
  -  Rising interest rates, an issuer's
     worsening financial condition or a drop
     in bond ratings can reduce the price of
     your units.
  -  Because the Fund is concentrated in
     hospital/health care bonds, adverse
     developments in this sector may affect
     the value of your units.
  -  Assuming no changes in interest rates,
     when you sell your units, they will
     generally be worth less than your cost
     because your cost included a sales fee.
  -  The Fund will receive early returns of
     principal if bonds are called or sold
     before they mature. If this happens your
     income will decline and you may not be
     able to reinvest the money you receive
     at as high a yield or as long a
     maturity.
</TABLE>

<TABLE>
<C>  <S>
 5.  IS THIS FUND APPROPRIATE FOR YOU?

     Yes, if you want monthly income free
     from regular federal income tax. You
     will benefit from a professionally
     selected and supervised portfolio whose
     risk is reduced by investing in bonds of
     several different issuers.
     The Fund is NOT appropriate for you if
     you want a speculative investment that
     changes to take advantage of market
     movements, if you do not want a
     tax-advantaged investment or if you
     cannot tolerate any risk.
</TABLE>

                                       3
<PAGE>

<TABLE>
<C>  <S>
     DEFINING YOUR INCOME
</TABLE>

<TABLE>
<C>  <S>                                           <C>
     WHAT YOU MAY EXPECT (PAYABLE ON THE 25TH DAY
     OF EACH MONTH):
     Regular Monthly Income per unit                $ 4.61
     Annual Income per unit                         $55.34
     RECORD DAY: 10th day of each month

     THESE FIGURES ARE ESTIMATES ON THE EVALUATION DATE;
     ACTUAL PAYMENTS MAY VARY.
</TABLE>

<TABLE>
<C>  <S>
 6.  WHAT ARE THE FUND'S FEES AND EXPENSES?

     This table shows the costs and expenses you may pay,
     directly or indirectly, when you invest in the Fund.

     INVESTOR FEES

     Maximum Sales Fee (Load) on new
     purchases (as a percentage of
     $1,000 invested)                            2.90%

     Employees of some of the Sponsors and their affiliates
     may be charged a reduced sales fee of no less than
     $5.00 per unit.

     The maximum sales fee is reduced if you invest at
     least $100,000, as follows:
</TABLE>

<TABLE>
<CAPTION>
                               YOUR MAXIMUM
                                SALES FEE
          IF YOU INVEST:         WILL BE:
          --------------       ------------
<C>  <S>                       <C>
     Less than $100,000            2.90%
     $100,000 to $249,999          2.65%
     $250,000 to $499,999          2.40%
     $500,000 to $999,999          2.15%
     $1,000,000 and over           1.90%

     Maximum Exchange Fee          1.90%
</TABLE>

<TABLE>
<C>  <S>
     ESTIMATED ANNUAL FUND OPERATING EXPENSES
</TABLE>

<TABLE>
<CAPTION>
                                                    AMOUNT
                                                   PER UNIT
                                                   --------
<C>  <S>                                          <C>
                                                    $ 0.64
     Trustee's Fee
                                                    $ 0.47
     Portfolio Supervision,
     Bookkeeping and
     Administrative Fees
     (including updating
     expenses)
                                                    $ 0.27
     Evaluator's Fee
                                                    $ 0.27
     Other Operating Expenses
                                                    ------
                                                    $ 1.65
     TOTAL
</TABLE>

<TABLE>
<C>  <S>
     The Sponsors historically paid updating
     expenses.
</TABLE>

<TABLE>
<C>  <S>
 7.  HOW HAVE SIMILAR FUNDS PERFORMED IN THE
     PAST?

     IN THE FOLLOWING CHART WE SHOW PAST
     PERFORMANCE OF PRIOR MUNICIPAL INSURED
     SERIES, WHICH HAD THE SAME INVESTMENT
     OBJECTIVES, STRATEGIES AND TYPES OF
     BONDS AS THIS FUND. These prior Insured
     Series were offered between January 5,
     1988 and October 17, 1996 and were
     outstanding on December 31, 1999. OF
     COURSE, PAST PERFORMANCE OF PRIOR SERIES
     IS NO GUARANTEE OF FUTURE RESULTS OF
     THIS FUND.

     AVERAGE ANNUAL COMPOUND TOTAL RETURNS
     FOR PRIOR SERIES
     REFLECTING ALL EXPENSES. FOR PERIODS
     ENDED 12/31/99.
</TABLE>

 -------------------------------------------------------------------

<TABLE>
 High                    2.89%     6.77%     5.49%      3.07     7.97%     6.08%
 <S>                    <C>       <C>       <C>       <C>       <C>       <C>
 Average                 -4.66      5.23      5.24     -2.64      6.31      5.83
 Low                     -13.33     2.74      5.04     -10.59     3.60      5.63
</TABLE>

 -----------------------------------------------------------

<TABLE>
 <S>                    <C>       <C>       <C>       <C>       <C>       <C>
 Average
 Sales fee               2.13%     5.32%     5.82%
</TABLE>

 -----------------------------------------------------

NOTE: ALL RETURNS REPRESENT CHANGES IN UNIT PRICE WITH DISTRIBUTIONS REINVESTED
 INTO THE MUNICIPAL FUND INVESTMENT ACCUMULATION PROGRAM.

<TABLE>
<C>  <S>
 8.  IS THE FUND MANAGED?

     Unlike a mutual fund, the Fund is not managed
     and bonds are not sold because of market
     changes. Rather, experienced
</TABLE>

<TABLE>
<C>  <S>
     Defined Asset Funds financial analysts
     regularly review the bonds in the Fund.
     The Fund may sell a bond if certain
     adverse credit or other conditions
     exist.
 9.  HOW DO I BUY UNITS?

     The minimum investment is one unit.

     You can buy units from any of the
     Sponsors and other broker-dealers. The
     Sponsors are listed later in this
     prospectus. Some banks may offer units
     for sale through special arrangements
     with the Sponsors, although certain
     legal restrictions may apply.
</TABLE>

                                       4
<PAGE>

<TABLE>
<C>  <S>
     UNIT PRICE PER UNIT              $955.30
     (as of December 31, 1999)

     Unit price is based on the net asset
     value of the Fund plus the sales fee. An
     amount equal to any principal cash, as
     well as net accrued but undistributed
     interest on the unit, is added to the
     unit price. An independent evaluator
     prices the bonds at 3:30 p.m. Eastern
     time every business day. Unit price
     changes every day with changes in the
     prices of the bonds in the Fund.

10.  HOW DO I SELL UNITS?

     You may sell your units at any time to
     any Sponsor or the Trustee for the net
     asset value determined at the close of
     business on the date of sale. You will
     not pay any other fee when you sell your
     units.

11.  HOW ARE DISTRIBUTIONS MADE AND TAXED?

     The Fund pays income monthly. In the
     opinion of bond counsel when each bond
     was issued, interest on the bonds in
     this Fund is generally 100% exempt from
     regular federal income tax.
     A portion of the income may also be
     exempt from state and local personal
     income taxes, depending on where you
     live.

     You will also receive principal payments
     if bonds are sold or called or mature,
     when the cash available is more than
     $5.00 per unit. You will be subject to
     tax on any gain realized by the Fund on
     the disposition of bonds.

12.  WHAT OTHER SERVICES ARE AVAILABLE?

     REINVESTMENT
     You will receive your monthly income in
     cash unless you choose to compound your
     income by reinvesting with no sales fee
     in the Municipal Fund Investment
     Accumulation Program, Inc. This program
     is an open-end mutual fund with a
     comparable investment objective, but
     those bonds generally will not be
     insured. Income from this program will
     generally be subject to state and local
     income taxes. FOR MORE COMPLETE
     INFORMATION ABOUT THE PROGRAM, INCLUDING
     CHARGES AND FEES, ASK THE TRUSTEE FOR
     THE PROGRAM'S PROSPECTUS. READ IT
     CAREFULLY BEFORE YOU INVEST. THE TRUSTEE
     MUST RECEIVE YOUR WRITTEN ELECTION TO
     REINVEST AT LEAST 10 DAYS BEFORE THE
     RECORD DAY OF AN INCOME PAYMENT.

     EXCHANGE PRIVILEGES
     You may exchange units of this Fund for
     units of certain other Defined Asset
     Funds. You may also exchange into this
     Fund from certain other funds. We charge
     a reduced sales fee on exchanges.
</TABLE>

                                       5
<PAGE>
- --------------------------------------------------------------------------------
    TAX-FREE VS. TAXABLE INCOME: A COMPARISON OF TAXABLE AND TAX-FREE YIELDS

<TABLE>
                                      EFFECTIVE
TAXABLE INCOME 2000*                  % TAX                                  TAX-FREE YIELD OF
  SINGLE RETURN      JOINT RETURN     BRACKET      3%        3.5%        4%        4.5%        5%        5.5%        6%
                                                                    IS EQUIVALENT TO A TAXABLE YIELD OF
<S>                <C>                <C>        <C>        <C>        <C>        <C>        <C>        <C>        <C>
- ---------------------------------------------------------------------------------------------------------------------------
$      0- 26,250   $      0- 43,850    15.00       3.53       4.12       4.71       5.29       5.88       6.47       7.06
- ---------------------------------------------------------------------------------------------------------------------------
$ 26,251- 63,550   $ 43,851-105,950    28.00       4.17       4.86       5.56       6.25       6.94       7.64       8.33
- ---------------------------------------------------------------------------------------------------------------------------
$ 63,551-132,600   $105,951-161,450    31.00       4.35       5.07       5.80       6.52       7.25       7.97       8.70
- ---------------------------------------------------------------------------------------------------------------------------
<S>                <C>                <C>        <C>        <C>        <C>        <C>        <C>        <C>        <C>
$132,601-288,350   $161,451-288,350    36.00       4.69       5.47       6.25       7.03       7.81       8.59       9.38
- ---------------------------------------------------------------------------------------------------------------------------
<S>                <C>                <C>        <C>        <C>        <C>        <C>        <C>        <C>        <C>
  OVER $288,350    OVER $288,350       39.60       4.97       5.79       6.62       7.45       8.28       9.11       9.93
- ---------------------------------------------------------------------------------------------------------------------------
<S>                <C>                <C>        <C>        <C>        <C>        <C>        <C>        <C>        <C>

<S>                <C>
TAXABLE INCOME 20
  SINGLE RETURN     6.5%
                      IS
                   EQUIVALENT
                     TO A
                   TAXABLE
                   YIELD OF
- -----------------
$      0- 26,250     7.65
- -----------------
$ 26,251- 63,550     9.03
- -----------------
$ 63,551-132,600     9.42
                   --------
- -----------------
$132,601-288,350    10.16
                   --------
- -----------------
  OVER $288,350     10.76
                   --------
- -----------------
</TABLE>

To compare the yield of a taxable security with the yield of a federally
tax-free security, find your taxable income and read across. The table
incorporates 2000 federal income tax rates and assumes that all income would
otherwise be taxed at a U.S. investor's highest tax rate. Yield figures are for
example only.

*Based upon net amount subject to federal income tax after deductions and
exemptions. This table does not reflect the possible effect of other tax
factors, such as alternative minimum tax, personal exemptions, the phase-out of
exemptions, itemized deductions, the possible partial disallowance of deductions
or state and local taxation. Consequently, investors are urged to consult their
own tax advisers in this regard.

                                       6
<PAGE>
WHAT YOU CAN EXPECT FROM YOUR INVESTMENT

MONTHLY INCOME

The Fund will pay you regular monthly income. Your monthly income may vary
because of:
  - elimination of one or more bonds from the Fund's portfolio because of calls,
    redemptions or sales;
  - a change in the Fund's expenses; or
  - the failure by a bond's issuer to pay interest.

Changes in interest rates generally will not affect your monthly income because
the portfolio is fixed.

Along with your monthly income, you will receive your share of any available
bond principal.

RETURN FIGURES

We cannot predict your actual return, which will vary with unit price, how long
you hold your investment and changes in the portfolio, interest income and
expenses.

ESTIMATED CURRENT RETURN equals the estimated annual cash to be received from
the bonds in the Fund less estimated annual Fund expenses, divided by the Unit
Price (including the maximum sales fee):

<TABLE>
<S>              <C>  <C>
Estimated Annual         Estimated
Interest Income   -   Annual Expenses
- -------------------------------------
             Unit Price
</TABLE>

ESTIMATED LONG TERM RETURN is a measure of the estimated return over the
estimated life of the Fund. Unlike Estimated Current Return, Estimated Long Term
Return reflects maturities, discounts and premiums of the bonds in the Fund. It
is an average of the yields to maturity (or in certain cases, to an earlier call
date) of the individual bonds in the portfolio, adjusted to reflect the Fund's
maximum sales fee and estimated expenses. We calculate the average yield for the
portfolio by weighting each bond's yield by its market value and the time
remaining to the call or maturity date.

Yields on individual bonds depend on many factors including general conditions
of the bond markets, the size of a particular offering and the maturity and
quality rating of the particular issues. Yields can vary among bonds with
similar maturities, coupons and ratings.

These return quotations are designed to be comparative rather than predictive.

RECORDS AND REPORTS

You will receive:
- - a monthly statement of income payments and any principal payments;
- - a notice from the Trustee when new bonds are deposited in exchange or
  substitution for bonds originally deposited;
- - an annual report on Fund activity; and
- - annual tax information. THIS WILL ALSO BE SENT TO THE IRS. YOU MUST REPORT THE
  AMOUNT OF TAX-EXEMPT INTEREST RECEIVED DURING THE YEAR.

You may request:
- - copies of bond evaluations to enable you to comply with federal and state tax
  reporting requirements; and
- - audited financial statements of the Fund.

You may inspect records of Fund transactions at the Trustee's office during
regular business hours.

                                       7
<PAGE>
THE RISKS YOU FACE

INTEREST RATE RISK

Investing involves risks, including the risk that your investment will decline
in value if interest rates rise. Generally, bonds with longer maturities will
change in value more than bonds with shorter maturities. Bonds in the Fund are
more likely to be called when interest rates decline. This would result in early
returns of principal to you and may result in early termination of the Fund. Of
course, we cannot predict how interest rates may change.

CALL RISK

Many bonds can be prepaid or "called" by the issuer before their stated
maturity.

For example, an issuer might call its bonds if it no longer needs the money for
the original purpose or, during periods of falling interest rates, if the
issuer's bonds have a coupon higher than current market rates. If the bonds are
called, your income will decline and you may not be able to reinvest the money
you receive at as high a yield or as long a maturity. An early call at par of a
premium bond will reduce your return.

REDUCED DIVERSIFICATION RISK

If many investors sell their units, the Fund will have to sell bonds. This could
reduce the diversification of your investment and increase your share of Fund
expenses.

LIQUIDITY RISK

The bonds will generally trade in the over-the-counter market. We cannot assure
you that a liquid trading market will exist, especially since current law may
restrict the Fund from selling bonds to any Sponsor. The value of the bonds, and
of your investment, may be reduced if trading in bonds is limited or absent.

CONCENTRATION RISK

When a certain type of bond makes up 25% or more of the portfolio, the Fund is
said to be "concentrated" in that bond type, which makes the Fund less
diversified.

Here is what you should know about the Fund's concentration in hospital and
health care bonds:
  - payment for these bonds depends on revenues from private third-party payors
    and government programs, including Medicare and Medicaid, which have
    generally undertaken cost containment measures to limit payments to
    healthcare providers;
  - hospitals face increasing competition resulting from hospital mergers and
    affiliations;
  - hospitals need to reduce costs as HMOs increase market penetration and
    hospital supply and drug companies raise prices;
  - hospitals and health care providers are subject to various legal claims by
    patients and others and are adversely affected by increasing costs of
    insurance;
  - many hospitals are aggressively buying physician practices and assuming risk
    contracts to gain market share. If revenues do not increase accordingly,
    this practice could reduce profits;
  - Medicare is changing its reimbursement system for nursing homes. Many
    nursing home providers are not sure how they will be treated. In many cases,
    the providers may receive lower reimbursements and these would have to cut
    expenses to maintain profitability; and

                                       8
<PAGE>
  - most retirement/nursing home providers rely on entrance fees for operating
    revenues. If people live longer than expected and turnover is lower than
    budgeted, operating revenues would be adversely affected by less than
    expected entrance fees.

Here is what you should know about the Fund's concentration in refunded bonds.
Refunded bonds are typically:
  - backed by direct obligations of the U.S. government; or
  - in some cases, backed by obligations guaranteed by the U.S. government and
    placed in escrow with an independent trustee;
  - noncallable prior to maturity; but
  - sometimes called for redemption prior to maturity.

Changes to the portfolio from bond redemptions, maturities and sales may affect
the Fund's concentration over time.

BOND QUALITY RISK

A reduction in a bond's rating may decrease its value and, indirectly, the value
of your investment in the Fund.

INSURANCE RELATED RISK

The bonds are backed by insurance companies (as shown under Defined Portfolio).
Insurance policies generally make payments only according to a bond's original
payment schedule and do not make early payments when a bond defaults or becomes
taxable. Although the federal government does not regulate the insurance
business, various state laws and federal initiatives and tax law changes could
significantly affect the insurance business. The claims-paying ability of the
insurance companies is generally rated A or better by Standard & Poor's or
another nationally recognized rating organization. The insurance company ratings
are subject to change at any time at the discretion of the rating agencies.

LITIGATION AND LEGISLATION RISKS

We do not know of any pending litigation that might have a material adverse
effect upon the Fund.

Future tax legislation could affect the value of the portfolio by:
  - limiting real property taxes,
  - reducing tax rates,
  - imposing a flat or other form of tax, or
  - exempting investment income from tax.

SELLING OR EXCHANGING UNITS

You can sell your units at any time for a price based on net asset value. Your
net asset value is calculated each business day by:
  - ADDING the value of the bonds, net accrued interest, cash and any other Fund
    assets;
  - SUBTRACTING accrued but unpaid Fund expenses, unreimbursed Trustee advances,
    cash held to buy back units or for distribution to investors and any other
    Fund liabilities; and
  - DIVIDING the result by the number of outstanding units.

Your net asset value when you sell may be more or less than your cost because of
sales fees, market movements and changes in the portfolio.

SPONSORS' SECONDARY MARKET

While we are not obligated to do so, we will buy back units at net asset value
without any other fee or charge. We may resell the

                                       9
<PAGE>
units to other buyers or to the Trustee. You should consult your financial
professional for current market prices to determine if other broker-dealers or
banks are offering higher prices.

We have maintained a secondary market continuously for over 28 years, but we
could discontinue it without prior notice for any business reason.

SELLING UNITS TO THE TRUSTEE

Regardless of whether we maintain a secondary market, you can sell your units to
the Trustee at any time by sending the Trustee a letter (with any outstanding
certificates if you hold unit certificates). You must properly endorse your
certificates (or execute a written transfer instrument with signatures
guaranteed by an eligible institution). Sometimes, additional documents are
needed such as a trust document, certificate of corporate authority, certificate
of death or appointment as executor, administrator or guardian.

Within seven days after your request and the necessary documents are received,
the Trustee will mail a check to you. Contact the Trustee for additional
information.

As long as we are maintaining a secondary market, the Trustee will sell your
units to us at a price based on net asset value. If there is no secondary
market, the Trustee may sell your units in the over-the-counter market for a
higher price, but it is not obligated to do so. In that case, you will receive
the net proceeds of the sale.

If the Fund does not have cash available to pay you for units you are selling,
the agent for the Sponsors will select bonds to be sold. Bonds will be selected
based on market and credit factors. These sales could be made at times when the
bonds would not otherwise be sold and may result in your receiving less than the
unit par value and also reduce the size and diversity of the Fund.

There could be a delay in paying you for your units:
  - if the New York Stock Exchange is closed (other than customary weekend and
    holiday closings);
  - if the SEC determines that trading on the New York Stock Exchange is
    restricted or that an emergency exists making sale or evaluation of the
    bonds not reasonably practicable; and
  - for any other period permitted by SEC order.

EXCHANGE OPTION

You may exchange units of certain Defined Asset Funds for units of this Fund at
a maximum exchange fee of 1.90%. You may exchange units of this Fund for units
of certain other funds at a reduced sales fee if your investment goals change.
To exchange units, you should talk to your financial professional about what
funds are exchangeable, suitable and currently available.

Normally, an exchange is taxable and you must recognize any gain or loss on the
exchange. However, the IRS may try to disallow a loss if the portfolios of the
two funds are not materially different; you should consult your own tax adviser.

                                       10
<PAGE>
We may amend or terminate this exchange option at any time without notice.

HOW THE FUND WORKS

PRICING

The price of a unit includes interest accrued on the bonds, less expenses, from
the most recent Record Day up to, but not including, the settlement date, which
is usually three business days after the purchase date of the unit.

A portion of the price of a unit consists of cash so that the Trustee can
provide you with regular monthly income. When you sell your units you will
receive your share of this cash.

EVALUATIONS

An independent Evaluator values the bonds on each business day (excluding
Saturdays, Sundays and the following holidays as observed by the New York Stock
Exchange: New Year's Day, Presidents' Day, Martin Luther King, Jr. Day, Good
Friday, Memorial Day, Independence Day, Labor Day, Thanksgiving and Christmas).
Bond values are based on current bid or offer prices for the bonds or comparable
bonds. In the past, the difference between bid and offer prices of publicly
offered tax-exempt bonds has ranged from 0.5% of face amount on actively traded
issues to 3.5% on inactively traded issues; the difference has averaged between
1 and 2%.

INCOME

The Trustee credits interest to an Income Account and other receipts to a
Capital Account. The Trustee may establish a Reserve Account by withdrawing from
these accounts amounts it considers appropriate to pay any material liability.
These accounts do not bear interest.

EXPENSES

The Trustee is paid monthly. It also benefits when it holds cash for the Fund in
non-interest bearing accounts. The Trustee may also receive additional amounts:
  - to reimburse the Trustee for the Fund's operating expenses;
  - for extraordinary services and costs of indemnifying the Trustee and the
    Sponsors;
  - costs of actions taken to protect the Fund and other legal fees and
    expenses;
  - expenses for keeping the Fund's registration statement current; and
  - Fund termination expenses and any governmental charges.

The Sponsors are currently reimbursed up to 55 CENTS per $1,000 face amount
annually for providing portfolio supervisory, bookkeeping and administrative
services and for any other expenses properly chargeable to the Fund. Legal,
typesetting, electronic filing and regulatory filing fees and expenses
associated with updating the Portfolio's registration statement yearly are also
now chargeable to the Portfolio. While this fee may exceed the amount of these
costs and expenses attributable to this Fund, the total of these fees for all
Series of Defined Asset Funds will not exceed the aggregate amount attributable
to all of these Series for any calendar year. The Fund also pays the Evaluator's
fees.

                                       11
<PAGE>
The Trustee's, Sponsors' and Evaluator's fees may be adjusted for inflation
without investors' approval.

The Sponsors will pay advertising and selling expenses at no charge to the Fund.
If Fund expenses exceed initial estimates, the Fund will owe the excess. The
Trustee has a lien on Fund assets to secure reimbursement of Fund expenses and
may sell bonds if cash is not available.

PORTFOLIO CHANGES

The Sponsors and Trustee are not liable for any default or defect in a bond.

Unlike a mutual fund, the portfolio is designed to remain intact and we may keep
bonds in the portfolio even if their credit quality declines or other adverse
financial circumstances occur. However, we may sell a bond in certain cases if
we believe that certain adverse credit conditions exist or if a bond becomes
taxable.

If we maintain a secondary market in units but are unable to sell the units that
we buy in the secondary market, we will redeem units, which may affect the
composition of the portfolio. Units offered in the secondary market may not
represent the same face amount of bonds that they did originally.

We decide whether or not to offer units for sale that we acquire in the
secondary market after reviewing:
  - diversity of the portfolio;
  - size of the Fund relative to its original size;
  - ratio of Fund expenses to income;
  - current and long-term returns;
  - degree to which units may be selling at a premium over par; and
  - cost of maintaining a current prospectus.

FUND TERMINATION

The Fund will terminate following the stated maturity or sale of the last bond
in the portfolio. The Fund may also terminate earlier with the consent of
investors holding 51% of the units or if total assets of the Fund have fallen
below 40% of the face amount of bonds deposited. We will decide whether to
terminate the Fund early based on the same factors used in deciding whether or
not to offer units in the secondary market.

When the Fund is about to terminate you will receive a notice, and you will be
unable to sell your units after that time. On or shortly before termination, we
will sell any remaining bonds, and you will receive your final distribution. Any
bond that cannot be sold at a reasonable price may continue to be held by the
Trustee in a liquidating trust pending its final sale.

You will pay your share of the expenses associated with termination, including
brokerage costs in selling bonds. This may reduce the amount you receive as your
final distribution.

CERTIFICATES

Certificates for units are issued on request. You may transfer certificates by
complying with the requirements for redeeming certificates, described above. You
can replace lost or mutilated certificates by

                                       12
<PAGE>
delivering satisfactory indemnity and paying the associated costs.

TRUST INDENTURE

The Fund is a "unit investment trust" governed by a Trust Indenture, a contract
among the Sponsors, the Trustee and the Evaluator, which sets forth their duties
and obligations and your rights. A copy of the Indenture is available to you on
request to the Trustee. The following summarizes certain provisions of the
Indenture.

The Sponsors and the Trustee may amend the Indenture without your consent:
  - to cure ambiguities;
  - to correct or supplement any defective or inconsistent provision;
  - to make any amendment required by any governmental agency; or
  - to make other changes determined not to be materially adverse to your best
    interest (as determined by the Sponsors).

Investors holding 51% of the units may amend the Indenture. Every investor must
consent to any amendment that changes the 51% requirement. No amendment may
reduce your interest in the Fund without your written consent.

The Trustee may resign by notifying the Sponsors. The Sponsors may remove the
Trustee without your consent if:
  - it fails to perform its duties and the Sponsors determine that its
    replacement is in your best interest; or
  - it becomes incapable of acting or bankrupt or its affairs are taken over by
    public authorities.

Investors holding 51% of the units may remove the Trustee. The Evaluator may
resign or be removed by the Sponsors and the Trustee without the consent of
investors. The resignation or removal of either becomes effective when a
successor accepts appointment. The Sponsors will try to appoint a successor
promptly; however, if no successor has accepted within 30 days after notice of
resignation, the resigning Trustee or Evaluator may petition a court to appoint
a successor.

Any Sponsor may resign as long as one Sponsor with a net worth of $2 million
remains and agrees to the resignation. The remaining Sponsors and the Trustee
may appoint a replacement. If there is only one Sponsor and it fails to perform
its duties or becomes bankrupt the Trustee may:
  - remove it and appoint a replacement Sponsor;
  - liquidate the Fund; or
  - continue to act as Trustee without a Sponsor.

Merrill Lynch, Pierce, Fenner & Smith Incorporated acts as agent for the
Sponsors.

The Trust Indenture contains customary provisions limiting the liability of the
Trustee, the Sponsors and the Evaluator.

LEGAL OPINION

Davis Polk & Wardwell, 450 Lexington Avenue, New York, New York 10017, as
special counsel for the Sponsors, has given an opinion that the units are
validly issued.

AUDITORS

Deloitte & Touche LLP, 2 World Financial Center, New York, New York 10281,
independent accountants, audited the

                                       13
<PAGE>
Statement of Condition included in this prospectus.

SPONSORS

The Sponsors are:
MERRILL LYNCH, PIERCE, FENNER & SMITH INCORPORATED (a wholly-owned subsidiary of
Merrill Lynch & Co., Inc.)
P.O. Box 9051,
Princeton, NJ 08543-9051
SALOMON SMITH BARNEY INC. (an indirectly wholly-owned subsidiary of Citigroup
Inc.)
388 Greenwich Street--23rd Floor,
New York, NY 10013
DEAN WITTER REYNOLDS INC. (a principal operating subsidiary of Morgan Stanley
Dean Witter & Co.)
Two World Trade Center--59th Floor,
New York, NY 10048
PRUDENTIAL SECURITIES INCORPORATED (an indirect wholly-owned subsidiary of the
Prudential Insurance Company of America)
One New York Plaza
New York, NY 10292
PAINEWEBBER INCORPORATED (a wholly-owned subsidiary of PaineWebber Group Inc.)
1285 Avenue of the Americas,
New York, NY 10019

Each Sponsor is a Delaware corporation and it, or its predecessor, has acted as
sponsor to many unit investment trusts. As a registered broker-dealer each
Sponsor buys and sells securities (including investment company shares) for
others (including investment companies) and participates as an underwriter in
various selling groups.

TRUSTEE

The Chase Manhattan Bank, Unit Investment Trust Department, 4 New York
Plaza--6th Floor, New York, New York 10004, is the Trustee. It is supervised by
the Federal Deposit Insurance Corporation, the Board of Governors of the Federal
Reserve System and New York State banking authorities.

UNDERWRITERS' AND SPONSORS' PROFITS

Underwriters receive sales charges when they sell units. The Sponsors also
realized a profit or loss on the initial deposit of the bonds. Any cash made
available by you to the Sponsors before the settlement date for those units may
be used in the Sponsors' businesses to the extent permitted by federal law and
may benefit the Sponsors.

A Sponsor or Underwriter may realize profits or sustain losses on bonds in the
Fund which were acquired from underwriting syndicates of which it was a member.

In maintaining a secondary market, the Sponsors will also realize profits or
sustain losses in the amount of any difference between the prices at which they
buy units and the prices at which they resell or redeem them.

PUBLIC DISTRIBUTION

The Sponsors do not intend to qualify units for sale in any foreign countries.
This prospectus does not constitute an offer to sell units in any country where
units cannot lawfully be sold.

CODE OF ETHICS

Merrill Lynch, as agent for the Sponsors, has adopted a code of ethics requiring
preclearance and reporting of personal securities transactions by its employees
with access to information on portfolio transactions. The goal of the code is to

                                       14
<PAGE>
prevent fraud, deception or misconduct against the Fund and to provide
reasonable standards of conduct.

YEAR 2000 ISSUES

Many computer systems were designed in such a way that they may be unable to
distinguish between the year 2000 and the year 1900 (commonly known as the "Year
2000 Problem"). We do not expect that the computer system changes necessary to
prepare for the Year 2000 will cause any major operational difficulties for the
Fund. The Year 2000 Problem may adversely affect the issuers of the bonds
contained in the Portfolio, but we cannot predict whether any impact will be
material to the Fund as a whole.

TAXES

The following summary describes some of the important income tax consequences of
holding units. It assumes that you are not a dealer, financial institution,
insurance company or other investor with special circumstances or subject to
special rules. You should consult your own tax adviser about your particular
circumstances.

At the date of issue of each bond, counsel for the issuer delivered an opinion
to the effect that interest on the bond is exempt from regular federal income
tax. However, interest may be subject to state and local taxes and may be taken
into account in determining your preference items for alternative minumum tax
purposes. Neither we nor our counsel have reviewed the issuance of the bonds,
related proceedings or the basis for the opinions of counsel for the issuers. We
cannot assure you that the issuer (or other users) have complied or will comply
with any requirements necessary for a bond to be tax-exempt. If any of the bonds
were determined not to be tax-exempt, you could be required to pay income tax
for current and prior years, and if the Fund were to sell the bond, it might
have to sell it at a substantial discount.

In the opinion of our counsel, under existing law:

GENERAL TREATMENT OF THE FUND AND YOUR INVESTMENT

The Fund will not be taxed as a corporation for federal income tax purposes, and
you will be considered to own directly your share of each bond in the Fund.

GAIN OR LOSS UPON DISPOSITION

When all or part of your share of a bond is disposed of (for example, when the
Fund sells, exchanges or redeems a bond or when you sell or exchange your
units), you will generally recognize capital gain or loss. Your gain, however,
will generally be ordinary income to the extent of any accrued "market
discount". Generally you will have market discount to the extent that your basis
in a bond when you purchase a unit is less than its stated redemption price at
maturity (or, if it is an original issue discount bond, the issue price
increased by original issue discount that has accrued on the bond before your
purchase). You should consult your tax adviser in this regard.

If your net long-term capital gains exceed your net short-term capital losses,
the excess may be subject to tax at a lower rate than ordinary income. Any
capital gain from the Fund will be long-term if you are considered to have held
your investment on each bond for more than one year and short-term otherwise. If
you are an individual and sell

                                       15
<PAGE>
your units after holding them for more than one year, you may be entitled to a
20% maximum federal tax rate on any resulting gains. Consult your tax adviser in
this regard. Because the deductibility of capital losses is subject to
limitations, you may not be able to deduct all of your capital losses.

YOUR BASIS IN THE BONDS

Your aggregate basis in the bonds will be equal to the cost of your units,
including any sales charges and the organizational expenses you pay, adjusted to
reflect any accruals of "original issue discount," "acquisition premium" and
"bond premium". You should consult your tax adviser in this regard.

EXPENSES

If you are not a corporate investor, you will not be entitled to a deduction for
your share of fees and expenses of the Fund. Also, if you borrowed money in
order to purchase or carry your units, you will not be able to deduct the
interest on this borrowing for federal income tax purposes. The IRS may treat
your purchase of units as made with borrowed money even if the money is not
directly traceable to the purchase of units.

STATE AND LOCAL TAXES

Under the income tax laws of the State and City of New York, the Fund will not
be taxed as a corporation. If you are a New York taxpayer, your income from the
Fund will not be tax-exempt in New York except to the extent that the income is
earned on bonds that are tax-exempt for New York purposes. Depending on where
you live, your income from the Fund may be subject to state and local taxation.
You should consult your tax adviser in this regard.

SUPPLEMENTAL INFORMATION

You can receive at no cost supplemental information about the Fund by calling
the Trustee. The supplemental information includes more detailed risk disclosure
about the types of bonds that may be in the Fund's portfolio, general risk
disclosure concerning any insurance securing certain bonds, and general
information about the structure and operation of the Fund. The supplemental
information is also available from the SEC.

                                       16
<PAGE>

          DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
          INSURED SERIES - 186

          REPORT OF INDEPENDENT ACCOUNTANTS

          The Sponsors, Trustee and Holders
          of Defined Asset Funds - Municipal Investment Trust Fund,
          Insured Series - 186:

          We have audited the accompanying statement of condition of Defined
          Asset Funds - Municipal Investment Trust Fund, Insured Series - 186,
          including the portfolio, as of December 31, 1999 and the related
          statements of operations and of changes in net assets for the years
          ended December 31, 1999, 1998 and 1997. These financial statements are
          the responsibility of the Trustee. 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. Securities owned at December 31, 1999, as shown
          in such portfolio, were confirmed to us by The Chase Manhattan Bank,
          the Trustee. An audit also includes assessing the accounting
          principles used and significant estimates made by the Trustee, 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 Defined
          Asset Funds - Municipal Investment Trust Fund, Insured Series - 186 at
          December 31, 1999 and the results of its operations and changes in its
          net assets for the above- stated years in conformity with generally
          accepted accounting principles.

          DELOITTE & TOUCHE LLP

          New York, N.Y.
          February 25, 2000


                                     D - 1.
<PAGE>

     DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
     INSURED SERIES - 186

     STATEMENT OF CONDITION
     As of December 31, 1999

<TABLE>
<S>                                                   <C>              <C>
TRUST PROPERTY:
  Investment in marketable securities
     at value (cost $ 9,600,404)(Note 1) .........                     $   9,854,773
  Accrued interest................................                           218,744
  Securities called for redemption
     at value (cost $55,275) (Note 5).............                            55,000
  Cash - principal ...............................                                98
                                                                       -------------
    Total trust property .........................                        10,128,615

LESS LIABILITY:
  Income advance from Trustee.....................                            78,289
                                                                       -------------

NET ASSETS, REPRESENTED BY:
  10,577 units of fractional undivided
     interest outstanding (Note 3) ...............    $   9,909,871

  Undistributed net investment income ............          140,455    $  10,050,326
                                                      -------------    =============

UNIT VALUE ($ 10,050,326 / 10,577 units)..........                     $      950.21
                                                                       =============
</TABLE>

                       See Notes to Financial Statements.


                                     D - 2.
<PAGE>

     DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
     INSURED SERIES - 186

     STATEMENTS OF OPERATIONS

<TABLE>
<CAPTION>
                                                           Years Ended December 31,
                                                     1999            1998            1997
                                                     ----            ----            ----
<S>                                          <C>              <C>               <C>
INVESTMENT INCOME:

  Interest income ........................    $   617,638      $   681,953       $   777,356
  Trustee's fees and expenses ............        (12,562)         (13,365)          (14,881)
  Sponsors' fees .........................         (4,561)          (4,445)           (4,537)
                                              ----------------------------------------------
  Net investment income ..................        600,515          664,143           757,938
                                              ----------------------------------------------

REALIZED AND UNREALIZED GAIN (LOSS)
  ON INVESTMENTS:
  Realized gain on
    securities sold or redeemed ..........         43,078          126,901            51,925
  Unrealized appreciation (depreciation)
    of investments .......................       (765,625)         (56,835)          328,485
                                              ----------------------------------------------
  Net realized and unrealized
    gain (loss) on investments ...........       (722,547)          70,066           380,410
                                              ----------------------------------------------

NET INCREASE (DECREASE) IN NET ASSETS
  RESULTING FROM OPERATIONS ..............    $  (122,032)     $   734,209       $ 1,138,348
                                              ==============================================
</TABLE>

                        See Notes to Financial Statements


                                     D - 3.
<PAGE>

     DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
     INSURED SERIES - 186

     STATEMENTS OF CHANGES IN NET ASSETS

<TABLE>
<CAPTION>
                                                           Years Ended December 31,
                                                     1999            1998            1997
                                                     ----            ----            ----
 <S>                                          <C>              <C>               <C>
OPERATIONS:
  Net investment income ..................    $   600,515      $   664,143       $   757,938
  Realized gain on
    securities sold or redeemed ..........         43,078          126,901            51,925
  Unrealized appreciation (depreciation)
    of investments .......................       (765,625)         (56,835)          328,485
                                              ----------------------------------------------
  Net increase (decrease) in net assets
    resulting from operations ............       (122,032)         734,209         1,138,348
                                              ----------------------------------------------
DISTRIBUTIONS TO HOLDERS (Note 2):
  Income  ................................       (601,357)        (665,613)         (761,482)
  Principal ..............................       (106,223)        (112,456)         (677,761)
                                              ----------------------------------------------
  Total distributions ....................       (707,580)        (778,069)       (1,439,243)
                                              ----------------------------------------------
SHARE TRANSACTIONS:
  Redemption amounts - income ............         (7,350)         (17,930)          (11,133)
  Redemption amounts - principal .........       (582,682)      (1,465,747)         (899,903)
                                              ----------------------------------------------
  Total share transactions ...............       (590,032)      (1,483,677)         (911,036)
                                              ----------------------------------------------

NET DECREASE IN NET ASSETS ...............     (1,419,644)      (1,527,537)       (1,211,931)

NET ASSETS AT BEGINNING OF YEAR ..........     11,469,970       12,997,507        14,209,438
                                              ----------------------------------------------
NET ASSETS AT END OF YEAR ................    $10,050,326      $11,469,970       $12,997,507
                                              ==============================================
PER UNIT:
  Income distributions during
    year .................................    $     55.64      $     56.33       $     57.85
                                              ==============================================
  Principal distributions during
    year .................................    $      9.93      $      9.72       $     50.93
                                              ==============================================
  Net asset value at end of
    year .................................    $    950.21      $  1,027.50       $  1,031.38
                                              ==============================================
TRUST UNITS:
  Redeemed during year ...................            586            1,439               896
  Outstanding at end of year .............         10,577           11,163            12,602
                                              ==============================================
</TABLE>

                       See Notes to Financial Statements.


                                     D - 4.
<PAGE>

     DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
     INSURED SERIES - 186

          NOTES TO FINANCIAL STATEMENTS

    1.    SIGNIFICANT ACCOUNTING POLICIES

          The Fund is registered under the Investment Company Act of 1940 as a
          Unit Investment Trust. The following is a summary of significant
          accounting policies consistently followed by the Fund in the
          preparation of its financial statements. The policies are in
          conformity with generally accepted accounting principles.

          (A)      Securities are stated at value as determined by the Evaluator
                   based on bid side evaluations for the securities.

          (B)      The Fund is not subject to income taxes. Accordingly, no
                   provision for such taxes is required.

          (C)      Interest income is recorded as earned.

    2.    DISTRIBUTIONS

          A distribution of net investment income is made to Holders each month.
          Receipts other than interest, after deductions for redemptions and
          applicable expenses, are also distributed periodically.

    3.    NET CAPITAL

<TABLE>
<S>                                                                     <C>
     Cost of 10,577 units at Date of Deposit .....................      $10,954,291
     Less sales charge ..........................................           492,941
                                                                         -----------
     Net amount applicable to Holders ...........................        10,461,350
     Redemptions of units - net cost of 4,423 units redeemed
       less redemption amounts (principal).......................          (103,715)
     Realized gain on securities sold or redeemed ...............           316,055
     Principal distributions ....................................        (1,017,913)
     Net unrealized appreciation of investments..................           254,094
                                                                         -----------

     Net capital applicable to Holders ..........................       $ 9,909,871
                                                                         ===========
</TABLE>

    4.    INCOME TAXES

          As of December 31, 1999, net unrealized appreciation of investments
          (including securities called for redemption), based on cost for
          Federal income tax purposes, aggregated $254,094, of which $667
          related to depreciated securities and $254,761 related to appreciated
          securities. The cost of investment securities for Federal income tax
          purposes was $9,655,679 at December 31, 1999.

    5.    SECURITIES CALLED FOR REDEMPTION

          $55,000 face amount of Iowa Fin. Auth. Single Family Mtge. Rfdg.
          Bonds, 1992 Ser. F (AMBAC Ins.) were redeemend on January 1, 2000.
          Such securities are valued at the amount of proceeds subsequently
          received.


                                     D - 5.
<PAGE>

     DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
     INSURED SERIES - 186

     PORTFOLIO
     As of December 31, 1999

<TABLE>
<CAPTION>

                                             Rating of                                            Optional
     Portfolio No. and Title of                Issues       Face                                 Redemption
            Securities                        (1) (4)       Amount    Coupon      Maturities(3) Provisions(3)    Cost      Value(2)
            -------------                    ---------  ----------- -----------   -----------   ------------  ----------  ---------

<S>                                          <C>        <C>         <C>           <C>          <C>          <C>         <C>
  1  Allegheny Cnty., PA, Hosp. Dev. Auth.,    AAA      $ 1,130,000    6.000  %     2023         11/01/02   $ 1,098,970 $ 1,100,564
     Hlth. Care Ctr. Rev. Rfdg. Bonds,                                                           @ 102.000
     Ser. 1992 B (Presbyterian Univ.
     Hlth. Sys., Inc. Proj.) (MBIA Ins.)

  2  City of Chicago, IL, Wastewater           AAA          710,000    6.350        2022(5)      01/01/03       715,914     755,192
     Transmission Rev. Bonds, Ser. 1992                                                          @ 102.000
     (Financial Guaranty Ins.)

  3  City of Houston, TX, Wtr. and Swr.        AAA        1,015,000    5.750        2015         12/01/02       971,396   1,014,939
     Sys. Jr. Lien Rev. Rfdg. Bonds,                                                             @ 102.000
     Ser. 1992 C (MBIA Ins.)

  4  City of Muscatine, IA, Elec. Rev.         AAA          490,000    6.125        2012         01/01/02       488,633     502,627
     Rdfg. Bonds, Ser. 1992 (AMBAC Ins)                                                          @ 102.000

  5  Dist. of Columbia Hosp. Imp.and Rfdg.     AAA        1,400,000    6.250        2019         07/15/02     1,390,984   1,390,592
     Rev. Bonds (Children's Hosp. Issue),                                                        @ 102.000
     Ser. 1992 A (Financial Guaranty Ins.)

  6  Intermountain Pwr. Agy., UT, Pwr.         AAA           65,000    5.000        2012         Currently       56,912      61,528
     Supply Rev. Rfdg. Bonds, 1987
     Ser. A (MBIA Ins.)

  7  Iowa Fin. Auth. Single Family Mtge.       AAA          630,000    6.500        2025         01/01/03       633,150     635,872
     Rfdg. Bonds, 1992 Ser. F (AMBAC Ins.)                                                       @ 102.000

  8  New Hampshire Higher Educl. and Hlth.     AAA        1,500,000    6.250        2020         07/01/02     1,500,000   1,502,325
     Fac. Auth. Rev. Rdfg. Bonds, Univ.                                                          @ 102.000
     Sys. of New Hampshire Issue, Ser. 1992
     (MBIA Ins.)

</TABLE>


                                     D - 6.
<PAGE>

     DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
     INSURED SERIES - 186

     PORTFOLIO
     As of December 31, 1999

<TABLE>
<CAPTION>

                                             Rating of                                            Optional
     Portfolio No. and Title of                Issues       Face                                 Redemption
            Securities                        (1) (4)       Amount    Coupon      Maturities(3) Provisions(3)    Cost      Value(2)
            -------------                    ---------  ----------- -----------   -----------   ------------  ----------  ---------

<S>                                          <C>        <C>         <C>           <C>          <C>          <C>         <C>
  9  Piedmont Mun. Pwr. Agy., SC, Elec. Rev.   AAA      $   605,000    6.300  %     2022(5)      01/01/03   $   607,517 $   643,369
     Bonds, 1992 Rfdg. Ser. (MBIA Ins.)                                                          @ 102.000

 10  Rhode Island Hlth. and Educl. Bldg.       AAA        1,145,000    6.250        2022(5)      04/01/03     1,129,726   1,215,715
     Corp. Higher Educl. Fac. Rev. Bonds                                                         @ 102.000
     Johnson and Wales Univ. Issue,
     Ser. 1992 A (Connie Lee Ins.)

                                                            300,000    6.250        2022         04/01/03       295,998     298,182
                                                                                                 @ 102.000

 11  Washington Hlth. Care Fac. Auth. Rev.     AAA          285,000    6.300        2022(5)      11/15/02       285,000     302,089
     Bonds, Ser. 1992 (Swedish Hosp. Med.                                                        @ 102.000
     Ctr., Seattle) (AMBAC Ins.)

 12  Wisconsin Hlth. and Educ. Fac. Auth.,     AAA          460,000    5.750        2022         08/15/03       426,204     431,779
     Wheaton Franciscan Svc., Inc. Sys.                                                          @ 102.000
     Rev. Bonds, Ser. 1992 (MBIA Ins.)

                                                          ---------                                           ---------   ---------
                                                        $ 9,735,000                                         $ 9,600,404 $ 9,854,773
                                                          =========                                           =========   =========
</TABLE>

                             See Notes to Portfolio.


                                     D - 7.
<PAGE>

     DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
     INSURED SERIES - 186

     NOTES TO PORTFOLIO
     As of December 31, 1999

    (1)   The ratings of the bonds are by Standard & Poor's Ratings Group, or by
          Moody's Investors Service, Inc. if followed by "(m)", or by Fitch
          Investors Service, Inc. if followed by "(f)"; "NR" indicates that this
          bond is not currently rated by any of the above-mentioned rating
          services. These ratings have been furnished by the Evaluator but not
          confirmed with the rating agencies.

    (2)   See Notes to Financial Statements.

    (3)   Optional redemption provisions, which may be exercised in whole or in
          part, are initially at prices of par plus a premium, then subsequently
          at prices declining to par. Certain securities may provide for
          redemption at par prior or in addition to any optional or mandatory
          redemption dates or maturity, for example, through the operation of a
          maintenance and replacement fund, if proceeds are not able to be used
          as contemplated, the project is condemned or sold or the project is
          destroyed and insurance proceeds are used to redeem the securities.
          Many of the securities are also subject to mandatory sinking fund
          redemption commencing on dates which may be prior to the date on which
          securities may be optionally redeemed. Sinking fund redemptions are at
          par and redeem only part of the issue. Some of the securities have
          mandatory sinking funds which contain optional provisions permitting
          the issuer to increase the principal amount of securities called on a
          mandatory redemption date. The sinking fund redemptions with optional
          provisions may, and optional refunding redemptions generally will,
          occur at times when the redeemed securities have an offering side
          evaluation which represents a premium over par. To the extent that the
          securities were acquired at a price higher than the redemption price,
          this will represent a loss of capital when compared with the Public
          Offering Price of the Units when acquired. Distributions will
          generally be reduced by the amount of the income which would otherwise
          have been paid with respect to redeemed securities and there will be
          distributed to Holders any principal amount and premium received on
          such redemption after satisfying any redemption requests for Units
          received by the Fund. The estimated current return may be affected by
          redemptions.

    (4)   All securities are insured, either on an individual basis or by
          portfolio insurance, by a municipal bond insurance company which has
          been assigned "AAA" claims paying ability by Standard and Poor's.
          Accordingly, Standard & Poor's has assigned a "AAA" rating to the
          securiities. Securities covered by portfolio insurance are rated "AAA"
          only as long as they remain in the Trust.

    (5)   Bonds with an aggregate face amount of $2,745,000 have been
          pre-refunded and are expected to be called for redemption on the
          optional redemption provision dates shown.


                                     D - 8.

<PAGE>

DEFINED ASSET FUNDS-SM-

<TABLE>
<S>                                      <C>
HAVE QUESTIONS ?                         MUNICIPAL INVESTMENT TRUST FUND
Request the most recent free             INSURED SERIES--186
Information Supplement                   (A Unit Investment Trust)
that gives more details about            ---------------------------------------
the Fund, by calling:                    This Prospectus does not contain
The Chase Manhattan Bank                 complete information about the
1-800-323-1508                           investment company filed with the
                                         Securities and Exchange Commission in
                                         Washington, D.C. under the:
                                         - Securities Act of 1933 (file no.
                                         33-49159) and
                                         - Investment Company Act of 1940 (file
                                         no. 811-1777).
                                         TO OBTAIN COPIES AT PRESCRIBED RATES--
                                         WRITE: Public Reference Section of the
                                         Commission
                                         450 Fifth Street, N.W., Washington,
                                         D.C. 20549-6009
                                         CALL: 1-800-SEC-0330.
                                         VISIT: http://www.sec.gov.
                                         ---------------------------------------
                                         No person is authorized to give any
                                         information or representations about
                                         this Fund not contained in this
                                         Prospectus or the Information
                                         Supplement, and you should not rely on
                                         any other information.
                                         ---------------------------------------
                                         When units of this Fund are no longer
                                         available, this Prospectus may be used
                                         as a preliminary prospectus for a
                                         future series, but some of the
                                         information in this Prospectus will be
                                         changed for that series.
                                         UNITS OF ANY FUTURE SERIES MAY NOT BE
                                         SOLD NOR MAY OFFERS TO BUY BE ACCEPTED
                                         UNTIL THAT SERIES HAS BECOME EFFECTIVE
                                         WITH THE SECURITIES AND EXCHANGE
                                         COMMISSION. NO UNITS CAN BE SOLD IN ANY
                                         STATE WHERE A SALE WOULD BE ILLEGAL.
                                                                     14380--3/00
</TABLE>
<PAGE>
                             DEFINED ASSET FUNDS--
                        MUNICIPAL INVESTMENT TRUST FUND
                                 INSURED SERIES
                       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 of Form S-6.

  The cross-reference sheet (incorporated by reference to the Cross-Reference
Sheet to the Registration Statement of Defined Asset Funds Municipal Insured
Series, 1933 Act File No. 33-54565).

    The Prospectus.

    The Signatures.

The following exhibits:

     1.1.1-- Form of Standard Terms and Conditions of Trust Effective as of
            October 21, 1993 (incorporated by reference to Exhibit 1.1.1 to the
            Registration Statement of Municipal Investment Trust Fund, Multi-
            state Series--48, 1933 Act File No. 33-50247).

    1.11.1-- Merrill Lynch Code of Ethics

    1.11.2-- Municipal Investment Trust Fund Code of Ethics

    4.1  --Consent of the Evaluator.

    5.1  --Consent of independent accountants.

    9.1  -- Information Supplement (incorporated by reference to Exhibit 9.1 to
           Amendment No. 1 to the Registration Statement of Municipal Investment
           Trust Fund, Multistate Series--409, 1933 Act File No. 333-81777).

                                      R-1
<PAGE>
                             DEFINED ASSET FUNDS--
                        MUNICIPAL INVESTMENT TRUST FUND
                              INSURED SERIES--186

                                   SIGNATURES

  PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THE REGISTRANT,
DEFINED ASSET FUNDS--MUNICIPAL INVESTMENT TRUST FUND, INSURED SERIES--186,
CERTIFIES THAT IT MEETS ALL OF THE REQUIREMENTS FOR EFFECTIVENESS OF THIS
REGISTRATION STATEMENT PURSUANT TO RULE 485(B) UNDER THE SECURITIES ACT OF 1933
AND HAS DULY CAUSED THIS REGISTRATION STATEMENT OR AMENDMENT TO THE REGISTRATION
STATEMENT TO BE SIGNED ON ITS BEHALF BY THE UNDERSIGNED THEREUNTO DULY
AUTHORIZED IN THE CITY OF NEW YORK AND STATE OF NEW YORK ON THE 8TH DAY OF
MARCH, 2000.

             SIGNATURES APPEAR ON PAGES R-3, R-4, R-5, R-6 AND R-7.

    A majority of the members of the Board of Directors of Merrill Lynch,
Pierce, Fenner & Smith Incorporated has signed this Registration Statement or
Amendment to the Registration Statement pursuant to Powers of Attorney
authorizing the person signing this Registration Statement or Amendment to the
Registration Statement to do so on behalf of such members.

    A majority of the members of the Board of Directors of Salomon Smith Barney
Inc. has signed this Registration Statement or Amendment to the Registration
Statement pursuant to Powers of Attorney authorizing the person signing this
Registration Statement or Amendment to the Registration Statement to do so on
behalf of such members.

    A majority of the members of the Board of Directors of Prudential Securities
Incorporated has signed this Registration Statement or Amendment to the
Registration Statement pursuant to Powers of Attorney authorizing the person
signing this Registration Statement or Amendment to the Registration Statement
to do so on behalf of such members.

    A majority of the members of the Executive Committee of the Board of
Directors of PaineWebber Incorporated has signed this Registration Statement or
Amendment to the Registration Statement pursuant to Powers of Attorney
authorizing the person signing this Registration Statement or Amendment to the
Registration Statement to do so on behalf of such members.

    A majority of the members of the Board of Directors of Dean Witter Reynolds
Inc. has signed this Registration Statement or Amendment to the Registration
Statement pursuant to Powers of Attorney authorizing the person signing this
Registration Statement or Amendment to the Registration Statement to do so on
behalf of such members.

                                      R-2
<PAGE>
               MERRILL LYNCH, PIERCE, FENNER & SMITH INCORPORATED
                                   DEPOSITOR

<TABLE>
<S>                                       <C>
By the following persons, who constitute  Powers of Attorney have been filed
  a majority of                             under
  the Board of Directors of Merrill         Form SE and the following 1933 Act
  Lynch, Pierce,                            File
  Fenner & Smith Incorporated:              Number: 333-70593
</TABLE>

     GEORGE A. SCHIEREN
     JOHN L. STEFFENS
     By J. DAVID MEGLEN
       (As authorized signatory for Merrill Lynch, Pierce,
       Fenner & Smith Incorporated and
       Attorney-in-fact for the persons listed above)

                                      R-3
<PAGE>
                           SALOMON SMITH BARNEY INC.
                                   DEPOSITOR

<TABLE>
<S>                                                           <C>
By the following persons, who constitute a majority of        Powers of Attorney
  the Board of Directors of Salomon Smith Barney Inc.:          have been filed
                                                                under the 1933 Act
                                                                File Numbers:
                                                                333-63417 and
                                                                333-63033
</TABLE>

     MICHAEL A. CARPENTER
     DERYCK C. MAUGHAN

     By GINA LEMON
       (As authorized signatory for
       Salomon Smith Barney Inc. and
       Attorney-in-fact for the persons listed above)

                                      R-4
<PAGE>
                       PRUDENTIAL SECURITIES INCORPORATED
                                   DEPOSITOR

<TABLE>
<S>                                                                     <C>
By the following persons, who constitute a majority of                  Powers of Attorney
  the Board of Directors of Prudential Securities                         have been filed
  Incorporated:                                                           under Form SE and
                                                                          the following 1933
                                                                          Act File Numbers:
                                                                          33-41631 and
                                                                          333-15919
</TABLE>

     ROBERT C. GOLDEN
     ALAN D. HOGAN
     A. LAURENCE NORTON, JR.
     LELAND B. PATON
     VINCENT T. PICA II
     MARTIN PFINSGRAFF
     HARDWICK SIMMONS
     LEE B. SPENCER, JR.
     BRIAN M. STORMS

     By RICHARD R. HOFFMANN
       (As authorized signatory for Prudential Securities
       Incorporated and Attorney-in-fact for the persons
       listed above)

                                      R-5
<PAGE>
                            PAINEWEBBER INCORPORATED
                                   DEPOSITOR

<TABLE>
<S>                                       <C>
By the following persons, who constitute  Powers of Attorney have been filed
  the Board of Directors of PaineWebber     under
  Incorporated:                             the following 1933 Act File
                                            Number: 33-55073
</TABLE>

     MARGO N. ALEXANDER
     TERRY L. ATKINSON
     BRIAN M. BAREFOOT
     STEVEN P. BAUM
     MICHAEL CULP
     REGINA A. DOLAN
     JOSEPH J. GRANO, JR.
     EDWARD M. KERSCHNER
     JAMES P. MacGILVRAY
     DONALD B. MARRON
     ROBERT H. SILVER
     MARK B. SUTTON
     By ROBERT E. HOLLEY
       (As authorized signatory for
       PaineWebber Incorporated
       and Attorney-in-fact for the persons listed above)

                                      R-6
<PAGE>
                           DEAN WITTER REYNOLDS INC.
                                   DEPOSITOR

<TABLE>
<S>                                       <C>
By the following persons, who constitute  Powers of Attorney have been filed
  a majority of                             under Form SE and the following 1933
  the Board of Directors of Dean Witter     Act File Numbers: 33-17085,
  Reynolds Inc.:                            333-13039, 333-47553 and 89045
</TABLE>

     BRUCE F. ALONSO
     RICHARD M. DeMARTINI
     RAYMOND J. DROP
     JAMES F. HIGGINS
     JOHN J. MACK
     MITCHELL M. MERIN
     STEPHEN R. MILLER
     PHILIP J. PURCELL
     JOHN H. SCHAEFER
     THOMAS C. SCHNEIDER
     ALAN A. SCHRODER
     ROBERT G. SCOTT
     By MICHAEL D. BROWNE
       (As authorized signatory for
       Dean Witter Reynolds Inc.
       and Attorney-in-fact for the persons listed above)

                                      R-7


                                                                  Exhibit 1.11.1

CONFIDENTIAL                                               AS OF [March 1, 2000]

                                  MERRILL LYNCH
                               DEFINED ASSET FUNDS

                                 CODE OF ETHICS


Section 1 - Purpose of the Code of Ethics

      This Code of Ethics ("Code") is intended to provide guidance to the
management and employees of the Defined Asset Funds unit ("DF") of Merrill
Lynch, Pierce, Fenner & Smith, Incorporated ("Firm") as to the minimum standards
of conduct in personal securities transactions that are consistent with the
Firm's responsibilities to its clients and the unitholders in the unit
investment trusts or advisory accounts ("Trusts") sponsored or advised by the
Firm, and to provide assurance that those persons are in a position to act in
the best interests of clients and the unitholders of the Trusts. The Code is
administered by DF Legal.

      The management and employees of DF have a duty to put the interests of the
Trusts' unitholders first, ahead of any personal interests in investing and
trading in securities. This Code is intended to ensure that personal trading be
conducted consistent with the Code and in such a manner as to avoid any actual
or potential conflicts of interest. Management and employees of DF have a
fundamental duty not to take inappropriate advantage of their positions of trust
and responsibility. Accordingly, all personal securities transactions of
management and employees of DF must comply with the requirements of this Code,
or risk the imposition of sanctions as set forth in Section 12 below.
Furthermore, all personal trading should avoid even the appearance of a conflict
of interest with the Firm's clients or the Trusts' unitholders.

      This Code is not intended to discourage personal securities investments or
sound personal investment programs on the part of persons who are subject to the
Code. The purpose of the Code is to provide guidance to ensure that personal
investing is consistent with the interests of our unitholders. The Code must be
read in conjunction with all of the Firm's policies relating to business
conduct, including prohibitions against trading on inside information generally,

<PAGE>

communicating inside information to others (including by e-mail) and as set
forth in the Merrill Lynch Defined Asset Funds Ethical Wall Policy.

      As more fully described below, this Code contains two general prohibitions
of personal securities transactions:

      (a)  Trading in a security during a period when DF is considering a
           recommendation or making a decision to purchase or sell any of that
           security for the account of a Trust and for a period of time after
           the Trust's purchase. Your trading at this time could take advantage
           of, avoid possible short-run market effects of, or have a negative
           effect on, the Trust's securities transactions and be inconsistent
           with Firm policy.

      (b)  Trading on the basis of material nonpublic information, or
           communicating this information to others who trade on the basis of
           such information ("tipping"). These trading or tipping practices are
           abusive of the securities markets, violates Federal and State law,
           and is a serious concern to market regulators and enforcement
           authorities. This activity is in direct contravention of Firm policy.

      A person covered by the requirements of this Code violates the Code if
they engage in these prohibited transactions directly or indirectly, such as
through a partnership, personal holding company or trust account over which such
person has investment control or in which the person holds a beneficial
interest, or if any member of the person's immediate family sharing the same
residence engages in the described transactions. This Code also applies to
transactions in derivative securities, such as options or futures, and unit
investment trusts and mutual funds sponsored by the Firm as well.

      Employees are required to have a reasonable understanding of and comply
with the policies of the Firm that are designed to ensure compliance with
applicable Federal and state laws, and rules of the Securities and Exchange
Commission and various self-regulatory organizations which may govern employees'
activities. Any person encountering evidence of activity that may violate
applicable statutes or regulations or provisions of this Code should


                                       2
<PAGE>

promptly report such evidence to the DF Compliance Director. Each person should
be sensitive not only to actual conflicts but also to the appearance of
conflicts. Conduct that violates this Code can harm not only the person
involved, but also the Firm's clients and the reputation of the Firm. Violations
of the Code may result in sanctions, including dismissal, and could involve
personal civil or criminal liability.

      Each employee and management person of DF will be given a copy of the Code
when he or she commences employment and annually thereafter, and each time will
be asked to sign a statement that he or she has received and read the Code, and
that he or she agrees to report all personal securities transactions as may be
required in this Code and as may be required by Firm policies. Any employee who
has any questions regarding any aspect of this Code or, whether a proposed act
or transaction involves a conflict of interest or material nonpublic
information, should speak to the Compliance Director. In addition, employees may
report any unethical behavior on a confidential basis through the HOTLINE
established by the Firm's General Counsel's Office. The hotline number is (800)
338-8954 . In New York State or outside the United States, the hotline can be
reached at (212) 449-9590.

Section 2 - Federal Securities Law Standards

      Rule 17j-1 under the Investment Company Act of 1940 ("Investment Company
Act") makes it unlawful for any affiliated person of any Trust sponsored by the
Firm (or any other registered investment company) or of any principal
underwriter for any such Trust in connection with that person's purchase or
sale, directly or indirectly, of securities that are "held or to be acquired"
(as defined in Section 3(i)) by any Trust:

      (a)   To employ any device, scheme, or artifice to defraud any Trust;

      (b)   To make to any Trust any untrue statement of a material fact or omit
            to state to any Trust such a material fact necessary in order to
            make the statements made, in light of the circumstances under which
            they are made, not misleading;


                                       3
<PAGE>

      (c)   To engage in any act, practice or course of business that operates
            or would operate as a fraud or deceit on any Trust; or

      (d)   To engage in any manipulative practices with respect to any Trust.

The Rule requires that the Trusts and each sponsor of the Trusts (i) adopt a
written code of ethics containing provisions reasonably necessary to prevent
certain persons (known as "Access Persons" -- defined in Section 3(a), below)
from engaging in any of the unlawful activities described above, and (ii) use
reasonable diligence and institute procedures necessary to prevent violations of
such code.

Section 3 - Definitions

      (a)   Any person described in (1) or (2), below, must comply with all
            provisions of this Code that apply to "Access Persons." Any person
            described in (1) also must comply with all provisions in this Code
            that apply to "Investment Personnel" (formerly "Decision Making
            Access Persons"). DF Legal will notify each person who is considered
            to be an Access Person or an Investment Person.

            (1)   The term "Investment Person" (or "Investment Personnel")
                  includes: (i) any employee of DF or of any company controlling
                  DF who, in connection with his or her regular functions or
                  duties, makes or participates in making recommendations
                  regarding the purchase, sale or holding of a security by or
                  for the account of any Trust or any accumulation account for
                  any Trust, and (ii) any natural person who controls DF and who
                  obtains information concerning recommendations made to any
                  Trust regarding the purchase, sale or holding of a security by
                  or for the account of any Trust or any accumulation account
                  for any Trust.


                                       4
<PAGE>

            (2)   The term "Access Person" includes any person who falls within
                  the definition of an "Investment Person" in paragraph (1),
                  above, and also (i) any employee of DF or of any company
                  controlling DF who, in connection with his or her regular
                  functions or duties, makes, participates in or obtains
                  information regarding the purchase or sale of a security by
                  any Trust or any accumulation account for any Trust, or whose
                  functions or duties related to the making of any
                  recommendations with respect to the purchases or sales and
                  (ii) any natural person who controls DF who obtains
                  information concerning recommendations made to any Trust
                  regarding the purchase, sale or holding of a security by or
                  for the account of any Trust or any accumulation account for
                  any Trust.

      (b)   A security is "being considered for purchase, sale or holding" when
            a recommendation to purchase, sell or hold a security has been made
            or communicated and, with respect to the person making the
            recommendation, when that person seriously considers making such a
            recommendation.

      (c)   "Beneficial ownership" of, or "beneficial interest" in, a security
            shall be interpreted in the same manner as it would be in
            determining whether a person is subject to the provisions of Section
            16 of the Securities Exchange Act of 1934 and the rules and
            regulations thereunder, except that it shall apply to all securities
            which an Access Person has or acquires. This means that an Access
            Person should consider himself or herself to be the beneficial owner
            of any securities in which he or she has a direct or indirect
            pecuniary interest. In addition, an Access Person should consider
            himself or herself the beneficial owner of securities held by his or
            her spouse, minor children, any relative living in the same
            household, or any other person by reason of any contract,
            arrangement, or understanding that provides him or her with sole or
            shared voting or investment power.


                                       5
<PAGE>

      (d)   "Control" shall have the same meaning as that set forth in Section
            2(a)(9) of the Investment Company Act. Section 2(a)(9) provides that
            "control" "means the power to exercise a controlling influence over
            the management or policies of a company, unless such power is solely
            the result of an official position with such company." Ownership by
            any person other than a natural person of 25% or more of a company's
            voting securities is presumed to give the holder of those securities
            control of the company. A person who owns less than 25% of the
            voting securities of a company is presumed not to control the
            company. Either of these two presumptions may be overcome by the
            facts and circumstances of the particular situation. For purposes of
            this definition, control of a company includes control of (1) a
            corporation, partnership, association, joint-stock company, trust,
            fund, any organized group of persons, whether incorporated or not;
            (2) a receiver, trustee in a case under title 11 of the United
            States Code or similar official, or any liquidating agent for any of
            the foregoing, in his capacity as such; or (3) an account that
            invests in securities.

      (e)   "Initial Public Offering" means an offering of securities registered
            under the Securities Act of 1933 (other than securities issued by an
            open-end management company or units issued by a unit investment
            trust registered under the Investment Company Act of 1940), the
            issuer of which, immediately before the registration, was not
            subject to the reporting requirements of Sections 13 or 15(d) of the
            Securities Exchange Act of 1934.

      (f)   "Private Placement" means an offering that is exempt from
            registration under the Securities Act of 1933 pursuant to Section
            4(2) or Section 4(6) or pursuant to Rule 504, Rule 505, or Rule 506
            under the Securities Act of 1933.

      (g)   "Purchase" or "sale" of a security includes, among other things, (i)
            the buying or writing of an option to purchase or sell a security,
            or (ii) an indirect purchase or sale by a person through a
            partnership, personal holding company or trust account


                                       6
<PAGE>

            over which such person has investment control or holds a beneficial
            interest, or by any member of the person's immediate family sharing
            the same residence.

      (h)   "Security" shall have the meaning set forth in Section 2(a)(36) of
            the Investment Company Act, except that (i) it shall also include
            any instrument commonly known as a derivative (including, but not
            limited to, any forward contract, future, swap, or option), and (ii)
            other than for purposes of pre-clearing securities issued in an
            Initial Public Offering or a Private Placement, it shall not include
            securities that are direct obligations of the U.S. Government,
            bankers' acceptances, bank certificates of deposit, commercial
            paper, high quality short-term debt instruments and shares of
            open-end investment companies.

      (i)   "Security Held or to be Acquired" means (i) any security which,
            within the most recent 15 days, (A) is or has been held by a Trust
            or (B) is being or has been considered for purchase on behalf of a
            Trust, and (ii) any option to purchase or sell, and any security
            convertible into or exchangeable for, a security which, within the
            most recent 15 days, (A) is or has been held by a Trust or (B) is
            being or has been considered for purchase on behalf of a Trust.

      (j)   "Trusts" means the unit investment trusts sponsored or underwritten
            by Merrill Lynch, Pierce, Fenner & Smith Incorporated.

Section 4 - Exempted Transactions

      The requirements of Section 5 of this Code, except for the requirement to
pre-clear securities issued in an Initial Public Offering or a Private
Placement, shall not apply to:

      (a)   A purchase or sale of securities effected in any account over which
            the Access Person has no direct or indirect influence, control, or
            beneficial interest.


                                       7
<PAGE>

      (b)   A purchase or sale of securities which are not eligible for purchase
            or sale by any of the Trusts.

      (c)   A purchase or sale of securities which is non-volitional on the part
            of the Access Person (for example, a purchase or sale effected by an
            investment manager for a pension or retirement plan, other than an
            individual retirement account, in which an Access Person is a
            beneficiary)(d) A purchase of securities which is made through an
            automatic dividend reinvestment plan.

      (e)   Purchases effected upon the exercise of rights issued by an issuer
            pro rata to all holders of a class of its securities, to the extent
            those rights were acquired from such issuer, and sales of such
            rights so acquired.

      (f)   A purchase or sale of securities issued by an open-end mutual fund.

      (g)   A purchase or sale of securities issued by any Defined Government
            Securities Income Funds.

      (h)   A purchase or sale of securities that are direct obligations of the
            U.S. government.

      (i)   A purchase or sale of bankers' acceptances, bank certificates of
            deposit, commercial paper, high quality short-term debt instruments.

      (j)   A purchase or sale of securities issued by any unit investment trust
            with 50 or more securities as of the initial date of deposit,
            including the S&P 500, Midcap and Defined Technology Series.

      (k)   Transactions occurring in the process of rolling over a Select
            Series Trust into the successor Series, resulting in a sale and a
            related purchase of Trust units.


                                       8
<PAGE>

      (l)   Crossover (e.g. Dow to International) and regular (e.g. Dow to Dow)
            rollover transactions in the Select Series.

      (m)   Subsequent reinvestments in an AIPS account; initial investment is
            not exempt.

      (n)   A purchase or sale of a security issued by any unit investment
            trust, including all RIC and grantor trusts, in which the underlying
            securities are traded on a national securities exchange, unless the
            Trust is a "Hot Issue". A "Hot Issue" is defined as a newly issued
            stock that is in great public demand. Hot Issues typically increase
            rapidly in price during their initial offering, since the demand
            exceeds the supply of shares.

Section 5 - Procedures Relating to Securities Transactions

      (a)   All officers and employees of DF are reminded that it is the Firm's
            policy that their securities accounts must generally be maintained
            at the Firm. See --- Policy Manual Section 2.01.4.

      (b)   The following procedures apply to every Access Person, including
            every Investment Person.

            (1)   Every Access Person must pre-clear each personal securities
                  transaction, including any acquisition of securities issued in
                  an Initial Public Offering or a Private Placement, by
                  contacting the Compliance Director by telephone, electronic
                  mail, in person, or by other means. Preclearance is valid only
                  on the day it is given. If an Access Person obtains
                  preclearance of a transaction, but waits until the next day to
                  trade, the Access Person must pre-clear the trade again. As
                  described in Section 6(a), below, after an Access Person has
                  effected a trade, the Access Person must file the Transactions
                  Required To Be Reported Under The Code Of Ethics


                                       9
<PAGE>

                  ("Transaction Form") form with the Compliance Director
                  describing the transaction. A copy of the Transaction Form is
                  attached.

            (2)   Every Access Person who owns, directly or indirectly,
                  securities obtained in a Private Placement must notify the
                  Compliance Director in writing prior to participating in a
                  Trust's subsequent consideration of an investment in that
                  issuer. The Trust's decision to invest in that issuer will be
                  subject to an independent review by DF investment persons who
                  do not have any personal interest in the issuer.

            (3)   No Access Person may purchase any security (i) seven calendar
                  days prior to and seven calendar days after the purchase of
                  the same security for initial deposit in any Trust or (ii) at
                  a time when he or she knows that the same security is being
                  considered for purchase by any Trust or any accumulation
                  account for any Trust.

            (4)   No Access Person may sell any security (i) seven calendar days
                  prior to and seven calendar days after the sale of the same
                  security as a result of a 22 Meeting and the termination or
                  rollover of any Trust, or (ii) at a time when he or she knows
                  that the same security is being considered for sale by any
                  Trust or any accumulation account for any Trust.

            (5)   For accounts that are not maintained at the Firm, every Access
                  Person must instruct his or her broker to send to the
                  Compliance Director (i) duplicate copies of confirmations of
                  that Access Person's personal securities transactions and (ii)
                  copies of all periodic account statements relating to that
                  Access Person's securities accounts within ten days of the end
                  of each calendar quarter.(1)

- ----------
(1) The Compliance Director receives daily reports of activity in employee
accounts maintained at the Firm. The Compliance Director also receives copies of
monthly account statements for employee accounts maintained at the Firm.


                                       10
<PAGE>

      (c)   Investment Personnel must observe the following procedures, in
            addition to the procedures described, above, in Section 5(b):

            (1)   An Investment Person must notify the Compliance Director in
                  writing of any intended purchase by any Trust or any
                  accumulation account for any Trust of a security which that
                  Investment Person beneficially owns.

            (2)   After a Trust has purchased a security for initial deposit
                  that an Investment Person also beneficially owns, the
                  Investment Person may not sell that security until seven
                  calendar days after the Trust's purchase of that security,
                  unless the Investment Person demonstrates to the satisfaction
                  of the Compliance Director a bona fide reason why such seven
                  calendar day period should be waived. Examples of such bona
                  fide reasons would be unexpected personal hardship occasioning
                  a need for funds or special year-end tax considerations. A
                  change in the Investment Person's investment objectives or
                  special new investment opportunities do not constitute
                  acceptable reasons for a waiver.

            (3)   After a Trust has sold a security as a result of a 22 Meeting
                  or the Trust's termination or rollover that a Investment
                  Personnel also beneficially owns, the Investment Person may
                  not purchase that security within seven calendar days unless
                  such Investment Person obtains preclearance approval by
                  notifying the Compliance Director in writing of his or her
                  intended purchase.

Section 6 - Reporting and Monitoring


                                       11
<PAGE>

      (a)   Access Person Transaction Reports. Every Access Person shall report
            to the Compliance Director the information described in Section
            6(d)(1) of this Code, below, in the Transaction Form attached to
            this Code, relating to transactions in any security of which that
            Access Person has, or by reason of such transaction acquires, any
            direct or indirect beneficial ownership in the security. Transaction
            Forms are not required for those exempted transactions, as described
            above in Section 4. The Compliance Director will retain a copy of
            each Transaction Form. In addition, for each approval granted to an
            Investment Person to acquire securities issued in an Initial Public
            Offering or a Private Placement, the compliance Director will make
            and retain a written record of the reasons for granting the
            approval.

      (b)   Initial and Annual Reports.

            (1)   Non-Access Person Employees. Each non-Access Person employee
                  shall complete, at the time they commence employment with DF
                  and at least once annually thereafter, the Employee Personal
                  Securities Accounts Report, as attached, concerning their
                  securities holdings and provide this information to the
                  Compliance Director.

            (2)   DF Access Persons. Each Access Person shall complete and
                  submit to the Compliance Director, within 10 days of becoming
                  an Access Person and by each January 30 thereafter, the Access
                  Person Personal Securities Holdings Report, which must include
                  the following information:

                  (i)   The title, number of shares and principal amount of each
                        security in which the Access Person has any direct or
                        indirect beneficial interest;


                                       12
<PAGE>

                  (ii)  The name of any broker, dealer or bank with whom the
                        Access Person maintains an account in which any
                        securities are held for the direct or indirect benefit
                        of the Access Person; and

                  (iii) The date the report is submitted by the Access Person.

                  In lieu of providing the required details about securities
                  holdings, Access Persons may confirm in writing the accuracy
                  of information maintained by the Compliance Director, as
                  explained more fully on the Access Person Personal Securities
                  Holdings Report.

      (c)   Access Person Quarterly Transaction Reports. In addition to
            preclearing securities transactions and submitting initial and
            annual holdings reports, each Access Person must also file with the
            Compliance Director on a quarterly basis a report describing every
            securities transaction that occurred during the quarter in any
            account that is not maintained with the Firm and in which the Access
            Person had any direct or indirect beneficial ownership. Each report
            must be filed within ten days after March 31, June 30, September 30
            and December 31 of each year.

            (1)   Securities Transactions. Each report must contain the
                  following information with respect to each securities
                  transactions during the quarter:

                  (i)   The date of the transaction, the title, the interest
                        rate and maturity date (if applicable), the number of
                        shares or units, or the principal amount of each
                        security involved;

                  (ii)  The nature of the transaction (e.g., purchase, sale or
                        any other type of acquisition or disposition);

                  (iii) The price at which the transaction was effected; and


                                       13
<PAGE>

                  (iv)  The name of the broker, dealer or bank with or through
                        whom the transaction was effected.

                  Alternatively, this requirement can be satisfied by providing
                  DF Legal with quarterly statements of any account that is not
                  maintained with the Firm, if provided within the required 10
                  day period.

            (2)   Brokerage Accounts. Each report must also disclose, for any
                  securities account established by the Access Person during the
                  quarter, the name of the broker, dealer or bank with whom the
                  Access Person established the account and the date the account
                  was established.

            (3)   Date of Submission. All quarterly transaction reports must
                  state the date submitted to DF Legal.

      (e)   Identification of Access Persons. DF Legal must identify all Access
            Persons who are under a duty to make reports and inform them of such
            duty.

      (f)   Review of Initial, Quarterly and Annual Reports. The Compliance
            Director or a designated person is responsible for reviewing each
            initial, quarterly and annual Access Person report.

Section 7 - Gifts

      All officers and employees of DF are reminded that they are subject to the
Firm's policies regarding the acceptance of gratuities. See Policy Manual
Section 2.01.9.

Section 8 - Service on Boards of Directors


                                       14
<PAGE>

      All officers and employees are reminded that they are subject to the
Firm's policies regarding service as a director of a company. See Policy Manual
Section 2.01.8.

Section 9 - Insider Trading

      No Access Person or employee of DF shall purchase or sell, directly or
indirectly, either personally or on behalf of others, any security while in
possession of material nonpublic information relating to that security or the
issuer of that security, or communicate material nonpublic information to others
in violation of the law. This prohibition extends to activities within and
outside such person's duties at DF.

      (a)   Information is generally considered material when there is a
            substantial likelihood that a reasonable investor would consider it
            important in making his or her investment decisions, or when it is
            reasonably certain to have a substantial effect on the price of a
            company's securities. Examples of this type of information include,
            but are not limited to, dividend changes, earnings estimates,
            changes in previously released earnings estimates, significant
            merger or acquisition proposals or agreements, major litigation,
            liquidation problems and extraordinary management developments.
            Material information need not relate to a company's business, but
            can include knowledge of a forthcoming report or recommendation
            concerning an issuer's securities that will have a significant
            market effect.

      (b)   Information is generally considered nonpublic until it has been
            effectively communicated to the market-place. One must be able to
            point to some fact to show that the information is generally public.
            Examples would include information found in a report filed with the
            Securities and Exchange Commission, appearing on the Dow Jones broad
            tape, or available through any electronic publication service or in
            publications of general circulation.


                                       15
<PAGE>

      (c)   It is unlawful not only to use inside information by trading while
            in possession of it but also to communicate (tip) such information
            to others who then trade on the basis of the information.

      (d)   Access Persons and employees of DF should consult with the
            Compliance Director if they have any questions about whether
            information in their possession is material nonpublic information
            subject to the prohibition against insider trading.

Section 10 - Exceptions

      The Compliance Director may, upon a written demonstration of hardship or
other significant factors, permit exceptions on a case-by-case basis, which
shall be in writing, to any of the prohibitions contained in this Code except
for the prohibition against insider trading described in Section 9, above. An
exception shall only be valid when provided in writing by the Compliance
Director.

Section 11 - Other Restrictions

      Certain transactions may be prohibited because of considerations relating
to the Firm's and DF's restricted lists. Securities are routinely placed on the
Firm's and DF's restricted lists for a variety of reasons. When a security
appears on the list, employees generally are not permitted to transact in that
security. The DF Ethical Wall Policy also describes instances where restrictions
are placed on employee trading.

Section 12 - Sanctions

      Upon discovering a violation of this Code, DF shall report such violation
to the Firm's Compliance Department which may take such steps as it deems
appropriate, including, among


                                       16
<PAGE>

other things, the issuance of a letter of censure or suspension or
recommendation of termination of the employment of the violator, or may refer
the matter to the appropriate regulatory or governmental authority.

Section 13 - Review of Code

      The Compliance Director of DF shall prepare an annual report relating to
this Code for submission to the Firm's Office of General Counsel. This report
shall summarize existing procedures concerning personal investing and any
changes in the procedures made during the past year; identify any violations
requiring significant remedial action during the past year; and identify any
recommended changes in the existing restrictions or procedures based upon DF's
experience under the Code, evolving industry practices or developments in
applicable laws or regulations.

Section 14 - Retention of Records

      The Compliance Director shall be responsible for maintaining the following
records in accordance with the requirements of Rule 17j-1 of the Investment
Company Act:

      (a)   A copy of the Code currently in effect and any versions of the Code
            in effect at any time within the past five years, as well as a copy
            of all codes of ethics for any Trust sponsored or co-sponsored by DF
            and any version of the codes in effect within the past five years,
            maintained in an easily accessible place;

      (b)   A record of any violations of the Code, and of any action taken as a
            result of the violation, maintained in an easily accessible place
            for at least five years after the end of the fiscal year in which
            the violation occurs;


                                       17
<PAGE>

      (c)   A copy of each (1) Non Access Person Securities Accounts Report, (2)
            Access Person Securities Holdings Report and (3) quarterly
            transaction report made by an Access Person, including any
            information provided in lieu of these reports, maintained for at
            least five years after the end of the fiscal year in which the
            report is made or the information is provided, the first two years
            in an easily accessible place;

      (d)   A record of all persons, currently or within the past five years,
            who are or were required to submit Access Person Securities Holdings
            Reports or quarterly transaction reports, or who are or were
            responsible for reviewing these reports, maintained in an easily
            accessible place;

      (e)   A record of any decision, and the reasons supporting the decision,
            to approve the acquisition of securities issued in an Initial Public
            Offering or Private Placement by an Investment Person, maintained
            for at least five years after the end of the fiscal year in which
            the approval is granted; and

      (f)   A copy of each Transaction Form, maintained for at least five years
            after the end of the fiscal year in which the approval is granted.

Section 15 - Compliance Director

      For purposes of this Code the Compliance Director shall be Teresa A.
Koncick or any other individual designated by the Compliance Director.

                                    * * * * *

      All questions concerning any requirements contained in this Code should be
directed to Ms. Koncick at 282-8717 or Debra Campanella at 282-8589.


                                       18
<PAGE>

                                NON-ACCESS PERSON
                           SECURITIES ACCOUNTS REPORT

NAME: ___________________________   DEPT/GROUP: _____________________

TITLE: ___________________________  TELEPHONE:   _____________________

1.    Do you maintain securities accounts with Merrill Lynch, Pierce, Fenner &
      Smith?

                        YES                     NO

      If yes, provide the following information for all accounts maintained with
      Merrill Lynch, Pierce, Fenner & Smith:

Type of                       Account                 Office(s) Where
Account(s)                    Number(s)               Maintained
- ----------                    ---------               ----------

- ------------------------------------------------------------------------------

- ------------------------------------------------------------------------------

- ------------------------------------------------------------------------------

2.    Do you maintain securities accounts outside Merrill Lynch?

                        YES                     NO

      If yes, provide the following information for all accounts maintained
      outside Merrill Lynch:

Type of                       Account                 Office(s) Where
Account(s)                    Number(s)               Maintained
- ----------                    ---------               ----------

- ------------------------------------------------------------------------------

- ------------------------------------------------------------------------------

- ------------------------------------------------------------------------------

The DF Division Compliance Director must be informed if you establish additional
accounts with either Merrill Lynch or with outside firms.

Return this report to the DF Legal Department

Signature:  ________________________________

Date:       ________________________________


                                       19
<PAGE>

                                  ACCESS PERSON
                           SECURITIES HOLDINGS REPORT

NAME: ___________________________   DEPT/GROUP: _____________________

TITLE: ___________________________  TELEPHONE:   _____________________

1.    Personal Securities Holdings. Do you have any direct or indirect
      beneficial interest in any securities (as defined in Section 3(h) of the
      Code)?

                        YES                     NO

      If yes, you must provide information called for on page 2 of this report.

2.    Merrill Lynch Accounts. Do you maintain securities accounts with Merrill
      Lynch, Pierce, Fenner & Smith in which any securities are held for your
      direct or indirect benefit?

                        YES                     NO

      If yes, provide the following information for all accounts maintained with
      Merrill Lynch:

Type of                       Account                 Office(s) Where
Account(s)                    Number(s)               Maintained
- ----------                    ---------               ----------

- ------------------------------------------------------------------------------

- ------------------------------------------------------------------------------

- ------------------------------------------------------------------------------

3.    Outside Accounts. Do you maintain securities accounts outside Merrill
      Lynch?

                        YES                     NO

      If yes, provide the following information for all accounts maintained
      outside Merrill Lynch:

Name of Broker,               Date Account            Account
Dealer or Bank                Established             Number
- --------------                -----------             ------

- ------------------------------------------------------------------------------

- ------------------------------------------------------------------------------

- ------------------------------------------------------------------------------

Reminder: The DF Division Compliance Director must be informed if you
established additional accounts with either Merrill Lynch or with outside firms.
In addition, if you establish an account with an outside firm, you must make
arrangements to have duplicate account statements sent to us within 10 days of
the end of each calendar quarter.

                                                            (Continue to page 2)


                                       20
<PAGE>

                                                                          Page 2

                                  ACCESS PERSON
                           SECURITIES HOLDINGS REPORT

                      LIST OF BENEFICIALLY OWNED SECURITIES

Please Circle One

1.    I have listed below all securities in which I have any direct or indirect
      beneficial ownership (as defined in Section 3(c) of the Code).

2.    I have attached a copy of my most recent account statement for each
      account which contains securities in which I have any direct or indirect
      beneficial ownership. Any beneficially-owned security that does not appear
      on my account statement(s) is listed below.

3.    I have received from the Compliance Director the attached Merrill Lynch
      monthly report(s) which contain(s) information about securities in which I
      have a direct or indirect beneficial ownership. Any beneficially-owned
      security that does not appear on my monthly report(s) is either included
      on the attached account statement(s) or listed below.

Title or                      Number of                     Principal
Name                          Shares                        Amount

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------

o     Please check here if additional pages listing your beneficially owned
      securities are attached and indicate the number of additional pages:
      _____.

o     Please check here if copies of account statements are attached and
      indicate the number of pages: _____.

My signature on this page certifies that the information about my personal
securities holdings listed on this report and any attached pages, if any, is
accurate, discloses all securities in which I have a direct or indirect
beneficial ownership, and is current as of the date I became an access person or
[December 31] of this past year, as applicable.

Signature:  ________________________________

Date:       ________________________________

Please return this report to the DF Legal Department


                                       21



                                                                  Exhibit 1.11.2

                               Code of Ethics for
                         Municipal Investment Trust Fund

A.    Introduction

      This Code of Ethics ("Code") has been prepared for the Municipal
Investment Trust Fund, (the "UIT"), as required by Rule 17j-1 under the
Investment Company Act of 1940 (the "1940 Act"). A unit investment trust, by its
nature, does not have any directors, officers or employees. This Code therefore
applies by reference to individuals associated with each of the UIT's sponsors
(each, a "Sponsor"). The Code establishes the minimum standards to which each
Sponsor's directors, officers and employees must abide. It is the responsibility
of each Sponsor to (1) approve this Code and (2) adopt its own code of ethics
incorporating these minimum standards, as well as any other provisions
necessary, taking into consideration the nature of the Sponsor's particular
business operations, to prevent employees from engaging in fraudulent or
manipulative conduct.

B.    Definitions

      For purposes of this Code:

      1.    Access Person means:

                  (a) Any director, officer, general partner or Advisory Person
                  of any of the UIT's Sponsors.

                        Note: If a Sponsor is primarily engaged in a business or
                        businesses other than Sponsoring the UIT or advising
                        other advisory clients, the term Access Person means any
                        director, officer, general partner or Advisory Person of
                        the Sponsor who, with respect to the UIT, makes any
                        recommendation, participates in the determination of
                        which recommendation will be made, or whose principal
                        function or duties relate to the determination of which
                        recommendation will be made, or who, in connection with
                        his or her duties, obtains any information concerning
                        recommendations on Covered Securities being made to the
                        UIT.

                        A Sponsor is "primarily engaged in a business or
                        businesses other than Sponsoring UITs or advising other
                        advisory clients" if, for each of its most recent

<PAGE>

                        three fiscal years or for the period of time since its
                        organization, whichever is less, the Sponsor derived, on
                        an unconsolidated basis, more than 50 percent of its
                        total sales and revenues and more than 50 percent of its
                        income (or loss), before income taxes and extraordinary
                        items, from the other business or businesses.

      2. Advisory Person means:

                  (a) Any employee of the UIT Sponsor (or of any company in a
                  control relationship to the UIT Sponsor) who, in connection
                  with his or her regular functions or duties, makes,
                  participates in, or obtains information regarding the purchase
                  or sale of Covered Securities by the UIT, or whose functions
                  relate to the making of any recommendations with respect to
                  the purchases or sales; and

                  (b) Any natural person in a control relationship to the UIT
                  Sponsor who obtains information concerning recommendations
                  made with regard to the purchase or sale of Covered Securities
                  by the UIT.

      3. Beneficial Ownership. For purposes of the Code, beneficial ownership is
      interpreted in the same manner as it would be under Rule 16a_1(a)(2) under
      the Securities Exchange Act of 1934 ("Exchange Act") in determining
      whether a person is the beneficial owner of a security for purposes of
      Section 16 of the Exchange Act and the rules and regulations thereunder.

      4. Control has the same meaning as in Section 2(a)(9) of the 1940 Act.

      5. Covered Security means a security as defined in Section 2(a)(36) of the
      1940 Act, except that it does not include:

            (a)   Direct obligations of the Government of the United States;

            (b)   Bankers' acceptances, bank certificates of deposit, commercial
                  paper and high quality short-term debt instruments, including
                  repurchase agreements; and

            (c)   Shares issued by open-end funds.


                                       2
<PAGE>

      6. Fund means any investment company registered under the 1940 Act.

      7. An Initial Public Offering means an offering of securities registered
      under the Securities Act of 1933 (the "Securities Act") (other than
      securities issued by an open-end management company or units issued by a
      unit investment trust registered under the Investment Company Act of
      1940), the issuer of which, immediately before the registration, was not
      subject to the reporting requirements of Sections 13 or 15(d) of the
      Exchange Act.

      8. Investment Personnel of a UIT Sponsor means:

            (a)   Any employee of the UIT Sponsor (or of any company in a
                  control relationship to the UIT Sponsor) who, in connection
                  with his or her regular functions or duties, makes or
                  participates in making recommendations regarding the purchase
                  or sale of securities by the UIT.

            (b)   Any natural person who controls the UIT Sponsor and who
                  obtains information concerning recommendations made regarding
                  the purchase or sale of securities by the UIT.

      9. A Limited Offering means an offering that is exempt from registration
      under the Securities Act pursuant to Section 4(2) or Section 4(6) or
      pursuant to Rule 504, Rule 505, or Rule 506 under the Securities Act.

      10. Purchase or sale of a Covered Security includes, among other things,
      the writing of an option to purchase or sell a Covered Security.

      11. Security Held or to be Acquired by a UIT means:

            (a)   Any Covered Security which, within the most recent 15 days:

                  (1) Is or has been held by the UIT; or

                  (2) Is being or has been considered by the UIT or its Sponsor
                  for purchase by the UIT; and

            (b) Any option to purchase or sell, and any security convertible
            into or exchangeable for, a Covered Security described above in
            Section B.11.(a) of the Code.


                                       3
<PAGE>

C.    Unlawful Actions - Generally

      It is unlawful for any affiliated person of any UIT Sponsor, in connection
with the purchase or sale, directly or indirectly, by the person of a Security
Held or to be Acquired by the UIT:

      1. To employ any device, scheme or artifice to defraud the UIT;

      2. To make any untrue statement of a material fact to the UIT or omit to
      state a material fact necessary in order to make the statements made to
      the UIT, in light of the circumstances under which they are made, not
      misleading;

      3. To engage in any act, practice or course of business that operates or
      would operate as a fraud or deceit on the UIT; or

      4. To engage in any manipulative practice with respect to the UIT.

D.    Requirements

      1.    Code of Ethics Adoption and Approval.

            (a) Each UIT Sponsor must adopt a written code of ethics containing
            the provisions set forth in this Code, as well as any other
            provisions reasonably necessary to prevent its Access Persons from
            engaging in any conduct prohibited by Section C of this Code.

            (b) Each UIT Sponsor must approve its own code of ethics and any
            material change to that code of ethics within six months of the
            material change.

            (c) Each UIT Sponsor must approve this Code. Each UIT Sponsor must
            also approve any material change to this Code no later than six
            months after the incorporation of the material change.

2. Administration of Code of Ethics. Each Sponsor must use reasonable diligence
and institute procedures reasonably necessary to prevent violations of this Code
and its own code of ethics.


                                       4
<PAGE>

E.    Reporting Requirements of Access Persons

      1. Reports Required. Unless excepted by Section E.2. of this Code, every
      Access Person of a UIT Sponsor, must report to that Sponsor:

            (a) Initial Holdings Reports. No later than 10 days after the person
            becomes an Access Person, the following information:

                  (i) The title, number of shares and principal amount of each
                  Covered Security in which the Access Person had any direct or
                  indirect beneficial ownership when the person became an Access
                  Person;

                  (ii) The name of any broker, dealer or bank with whom the
                  Access Person maintained an account in which any securities
                  were held for the direct or indirect benefit of the Access
                  Person as of the date the person became an Access Person; and

                  (iii) The date that the report is submitted by the Access
                  Person.

            (b) Quarterly Transaction Reports. No later than 10 days after the
            end of every calendar quarter, the following information:

                  (i) With respect to any transaction during the quarter in a
                  Covered Security in which the Access Person had any direct or
                  indirect beneficial ownership:

                        (1) The date of the transaction, the title, the interest
                        rate and maturity date (if applicable), the number of
                        shares and the principal amount of each Covered Security
                        involved;

                        (2) The nature of the transaction (i.e., purchase, sale
                        or any other type of acquisition or disposition);

                        (3) The price of the Covered Security at which the
                        transaction was effected;

                        (4) The name of the broker, dealer or bank with or
                        through which the transaction was effected; and


                                       5
<PAGE>

                        (5) The date that the report is submitted by the Access
                        Person.

                  (ii) With respect to any account established by the Access
                  Person in which any securities were held during the quarter
                  for the direct or indirect benefit of the Access Person:

                        (1) The name of the broker, dealer or bank with whom the
                        Access Person established the account;

                        (2) The date the account was established; and

                        (3) The date that the report is submitted by the Access
                        Person.

                  (c) Annual Holdings Reports. Annually, the following
                  information (which information must be current as of a date no
                  more than 30 days before the report is submitted):

                        (i) The title, number of shares and principal amount of
                        each Covered Security in which the Access Person had any
                        direct or indirect beneficial ownership;

                        (ii) The name of any broker, dealer or bank with whom
                        the Access Person maintains an account in which any
                        securities are held for the direct or indirect benefit
                        of the Access Person; and

                        (iii) The date that the report is submitted by the
                        Access Person.

      2. Exceptions from Reporting Requirements

                  (a) An Access Person to a UIT Sponsor need not make a report
                  under Section E.1 of this Code with respect to transactions
                  effected for, and Covered Securities held in, any account over
                  which the Access Person has no direct or indirect influence or
                  control.

                  (b) An Access Person to a UIT Sponsor need not make a
                  quarterly transaction report to the Sponsor under Section
                  E.1.(b) of this Code if all the information in the report


                                       6
<PAGE>

                  would duplicate information required to be recorded under Rule
                  204_2(a)(12) or Rule 204_2(a)(13) under the Investment
                  Advisers Act of 1940.

                  (c) An Access Person to a UIT Sponsor need not make a
                  quarterly transaction report under paragraph E.1.(b) of this
                  section if the report would duplicate information contained in
                  broker trade confirmations or account statements received by
                  the Sponsor with respect to the Access Person in the time
                  period required by Section E.1.(b), if all of the information
                  required by that provision is contained in the broker trade
                  confirmations or account statements, or in the records of the
                  Sponsor.

            3. Review of Reports. Each UIT Sponsor to which reports are required
            to be made by Section E.1. of this Code must institute procedures by
            which appropriate management or compliance personnel review these
            reports.

            4. Notification of Reporting Obligation. Each UIT Sponsor to which
            reports are required to be made by Section E.1. of this Code must
            identify all Access Persons who are required to make these reports
            and must inform those Access Persons of their reporting obligation.

            5. Disclaimer of Beneficial Ownership. Any report required by
            Section E.1 of this Code may contain a statement that the report
            will not be construed as an admission that the person making the
            report has any direct or indirect beneficial ownership in the
            Covered Security to which the report relates.

            6. Pre-approval of Investments in IPOs and Limited Offerings.
            Investment Personnel of each UIT Sponsor must obtain approval from
            their respective Sponsor before directly or indirectly acquiring
            beneficial ownership in any securities issued in any Initial Public
            Offering or Limited Offering.

F.     Recordkeeping Requirements

      Each UIT Sponsor must, at its principal place of business, maintain
records in the manner and to the extent set out in this Section F of the Code,
and must make these records available for examination by the SEC:


                                       7
<PAGE>

      1. The Code. A copy of each code of ethics for the Sponsor that is in
      effect, or at any time within the past five years was in effect, as well
      as a copy of this code and any version of this code in effect within the
      past five years, must be maintained in an easily accessible place;

      2. Code Violations. A record of any violation of the Sponsor's code of
      ethics, and of any action taken as a result of the violation, must be
      maintained in an easily accessible place for at least five years after the
      end of the fiscal year in which the violation occurs;

      3. Access Person Reports. A copy of each report made by an Access Person
      as required by Section E.1. of the Code, including any information
      provided in lieu of the reports under Section E.2.(c) of the Code, must be
      maintained for at least five years after the end of the fiscal year in
      which the report is made or the information is provided, the first two
      years in an easily accessible place;

      4. Reporting Persons and Reviewers. A record of all persons, currently or
      within the past five years, who are or were required to make reports under
      Section E.1. of the Code, or who are or were responsible for reviewing
      these reports, must be maintained in an easily accessible place; and

      5. Transaction Approvals. A record of any decision, and the reasons
      supporting the decision, to approve the acquisition by investment
      personnel of any securities issued in an Initial Public Offering or a
      Limited Offering, must be maintained for at least five years after the end
      of the fiscal year in which the approval is granted.


                                       8



                                                                     EXHIBIT 4.1

                               STANDARD & POOR'S
                    A DIVISION OF THE McGRAW-HILL COMPANIES
                                  J. J. KENNY
                                  65 BROADWAY
                           NEW YORK, N.Y. 10006-2551
                            TELEPHONE (212) 770-4422
                                FAX 212/797-8681

                                                      March 8, 2000

Frank A. Ciccotto, Jr
Vice President
Tax-Exempt Evaluations

<TABLE>
<S>                                       <C>
Merrill Lynch, Pierce, Fenner & Smith
Incorporated
Defined Asset Funds
P.O. Box 9051
Princeton, New Jersey 08543-9051

The Chase Manhattan Bank
4 New York Plaza--6th Floor
New York, New York 10004
</TABLE>

RE: DEFINED ASSET FUNDS--MUNICIPAL INVESTMENT TRUST FUND,
    INSURED SERIES--186

Gentlemen:

  We have examined the post-effective Amendment to the Registration Statement
File No. 33-49159 for the above-captioned trust. We hereby acknowledge that
Kenny S&P Evaluation Services, a division of J. J. Kenny Co., 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 J. J.
Kenny Co., 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 copies of this letter with the Securities
and Exchange Commission.

                                                      Sincerely,
                                                      FRANK A. CICCOTTO
                                                      Vice President



                                                                     Exhibit 5.1
                       CONSENT OF INDEPENDENT ACCOUNTANTS

The Sponsors and Trustee of
Defined Asset Funds--Municipal Investment Trust Fund--Insured Series--186

We consent to the use in this Post-Effective Amendment No. 8 to Registration
Statement No. 33-49159 of our opinion dated February 25, 2000 appearing in the
Prospectus, which is part of such Registration Statement, and to the reference
to us under the heading "Miscellaneous--Auditors" in such Prospectus.

DELOITTE & TOUCHE LLP
New York, N.Y.
March 8, 2000



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