DEFINED ASSET FUNDS MUNICIPAL INVT TR FD PENNSYLVANIA SER 12
497, 2000-04-20
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                             DEFINED ASSET FUNDS--REGISTERED TRADEMARK--
                             ------------------------------
                             ----------------------

                           MUNICIPAL INVESTMENT TRUST FUND
                           PENNSYLVANIA SERIES--12
                           (A UNIT INVESTMENT TRUST)
                           -  PENNSYLVANIA PORTFOLIO
                           -  PORTFOLIOS OF LONG-TERM MUNICIPAL BONDS
                           -  DESIGNED TO BE FREE OF REGULAR FEDERAL INCOME TAX
                           -  EXEMPT FROM SOME STATE TAXES
                           -  MONTHLY DISTRIBUTIONS

SPONSORS:
MERRILL LYNCH,             -----------------------------------------------------
PIERCE, FENNER & SMITH     The Securities and Exchange Commission has not
INCORPORATED               approved or disapproved these Securities or passed
PRUDENTIAL SECURITIES      upon the adequacy of this prospectus. Any
INC.                       representation to the contrary is a criminal offense.
DEAN WITTER REYNOLDS INC.  Prospectus dated April 21, 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 JANUARY 31, 2000, THE
EVALUATION DATE.

<TABLE>
<S>                                    <C>
CONTENTS
                                       PAGE
                                       ---
Pennsylvania Portfolio--
  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
  State Concentration Risk...........    9
  Bond Quality Risk..................    9
  Insurance Related Risk.............    9
  Litigation and Legislation Risks...   10
Selling or Exchanging Units..........   10
  Sponsors' Secondary Market.........   10
  Selling Units to the Trustee.......   10
  Exchange Option....................   11
How The Fund Works...................   11
  Pricing............................   11
  Evaluations........................   11
  Income.............................   11
  Expenses...........................   12
  Portfolio Changes..................   12
  Fund Termination...................   13
  Certificates.......................   13
  Trust Indenture....................   13
  Legal Opinion......................   14
  Auditors...........................   14
  Sponsors...........................   14
  Trustee............................   14
  Underwriters' and Sponsors'
    Profits..........................   14
  Public Distribution................   15
  Code of Ethics.....................   15
  Year 2000 Issues...................   15
Taxes................................   15
Supplemental Information.............   17
Financial Statements.................  D-1
</TABLE>

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

PENNSYLVANIA PORTFOLIO--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
     and some state and local taxes by
     investing in a fixed portfolio
     consisting primarily of long term
     municipal revenue bonds issued by the
     Commonwealth of Pennsylvania and its
     local governments and authorities.

 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 9
     long-term tax-exempt municipal bonds
     with an aggregate face amount of
     $6,214,000.
  -  The Fund is a unit investment trust
     which means that, unlike a mutual fund,
     the Portfolio is not managed.
  -  When the bonds were initially deposited
     they were rated A or better by Standard
     & Poor's, Moody's or Fitch. THE QUALITY
     OF THE BONDS MAY CURRENTLY BE LOWER.
  -  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.
  -  The Fund is concentrated in refunded
     bonds.
  -  30% of the bonds are insured by
     insurance companies that guarantee
     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>
  / / General Obligation                11%
<S>                                 <C>
  / / Refunded Bonds                    87%
  / / Universities/Colleges             2%
</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.

  -  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.

  -  In addition, 9% of the bonds are
     currently unrated.
</TABLE>

<TABLE>
<C>  <S>
     ALSO, THE PORTFOLIO IS CONCENTRATED IN
     BONDS OF PENNSYLVANIA SO IT IS LESS
     DIVERSIFIED THAN A NATIONAL FUND AND IS
     SUBJECT TO RISKS PARTICULAR TO
     PENNSYLVANIA WHICH ARE BRIEFLY DESCRIBED
     UNDER STATE CONCENTRATION RISKS LATER IN
     THIS PROSPECTUS.
</TABLE>

                                       3
<PAGE>
<TABLE>
<C>  <S>
 5.  IS THIS FUND APPROPRIATE FOR YOU?

     Yes, if you want federally tax-free
     income. 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>

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

<TABLE>
<C>  <S>                                           <C>
     WHAT YOU MAY EXPECT (Payable on the 25th day
     of the month to holders of record on the
     10th day of the month):
     Regular Monthly Income per unit                $ 2.84
     Annual Income per unit:                        $34.16
     THESE FIGURES ARE ESTIMATES DETERMINED ON THE
     EVALUATION DAY; 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 pay 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>
                                                    $0.41
     Trustee's Fee
                                                    $0.20
     Portfolio Supervision,
     Bookkeeping and
     Administrative Fees
     (including updating
     expenses)
                                                    $0.34
     Evaluator's Fee
                                                    $0.54
     Other Operating Expenses
                                                    -----
                                                    $1.49
     TOTAL
</TABLE>

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

 7.  HOW HAVE SIMILAR FUNDS PERFORMED IN THE PAST?

     IN THE FOLLOWING CHART WE SHOW PAST PERFORMANCE
     OF PRIOR PENNSYLVANIA PORTFOLIOS, WHICH HAD
     INVESTMENT OBJECTIVES, STRATEGIES AND TYPES OF
     BONDS SUBSTANTIALLY SIMILAR TO THIS FUND. THESE
     PRIOR SERIES DIFFERED IN THAT THEY CHARGED A
     HIGHER SALES FEE. These prior Pennsylvania
     Series were offered between May 19, 1988 and
     September 13, 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                    0.92%     6.43%     5.46%     2.00%     7.62%     6.05%
 <S>                    <C>       <C>       <C>       <C>       <C>       <C>
 Average                 -3.94      5.10      5.25     -2.10      6.16      5.82
 Low                     -13.31     3.07      5.12     -10.52     3.74      5.71
</TABLE>

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

<TABLE>
 <S>                    <C>       <C>       <C>       <C>       <C>       <C>
 Average
 Sales fee               1.94%     5.22%     5.66%
</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 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.
</TABLE>

                                       4
<PAGE>

<TABLE>
<C>  <S>
 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.

     UNIT PRICE PER UNIT              $622.38
     (as of January 31, 2000)

     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.
</TABLE>

<TABLE>
<C>  <S>
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. Your income
     may also be exempt from some Pennsylvania
     state and local personal income taxes if
     you live in Pennsylvania.
     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 income in cash
     unless you choose to compound your income
     by reinvesting at no sales fee in the
     Municipal Fund Investment Accumulation
     Program, Inc. This program is an open-end
     mutual fund with a comparable investment
     objective. 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

                           FOR PENNSYLVANIA RESIDENTS
- --------------------------------------------------------------------------------
<TABLE>
<CAPTION>
                                            COMBINED
                                            EFFECTIVE
TAXABLE INCOME 2000*                        TAX RATE                           TAX-FREE YIELD OF
    SINGLE RETURN         JOINT RETURN          %          3%        3.5%        4%        4.5%        5%        5.5%
<S>                     <C>                 <C>         <C>        <C>        <C>        <C>        <C>        <C>
                                                                      IS EQUIVALENT TO A TAXABLE YIELD OF

<CAPTION>

TAXABLE INCOME 2000*    TAX-FREE YIELD OF
    SINGLE RETURN         6%        6.5%        7%        7.5%        8%
<S>                    <C>        <C>        <C>        <C>        <C>
                       IS EQUIVALENT TO A
                        TAXABLE YIELD OF
</TABLE>

- --------------------------------------------------------------------------------
<TABLE>
<S>                     <C>                 <C>        <C>        <C>        <C>        <C>        <C>        <C>        <C>
  $      0- 26,250      $      0- 43,850     17.38       3.63       4.24       4.84       5.45       6.05       6.66       7.26
  $ 26,251- 63,550      $ 43,851-109,950     30.02       4.29       5.00       5.72       6.43       7.14       7.86       8.57
  $ 63,551-132,600      $105,951-161,450     32.93       4.47       5.22       5.96       6.71       7.46       8.20       8.95
  $132,601-288,350      $161,451-288,350     37.79       4.82       5.63       6.43       7.23       8.04       8.84       9.65
OVER $288,350           OVER $288,350        41.29       5.11       5.96       6.81       7.66       8.52       9.37      10.22

<S>                    <C>        <C>        <C>        <C>
  $      0- 26,250       7.87       8.47       9.08       9.68
  $ 26,251- 63,550       9.29      10.00      10.72      11.43
  $ 63,551-132,600       9.69      10.44      11.18      11.93
  $132,601-288,350      10.45      11.25      12.06      12.86
OVER $288,350           11.07      11.92      12.77      13.63
</TABLE>

To compare the yield of a taxable security with the yield of a tax-free
security, find your taxable income and read across. The table incorporates 2000
federal and applicable State income tax rates and assumes that all income would
otherwise be taxed at the 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 or the possible partial disallowance of
deductions. 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 income because the
portfolio is fixed.

Along with your 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, some bonds may be required to be called pursuant to mandatory
sinking fund provisions.

Also, an issuer might call its bonds during periods of falling interest rates,
if the issuer's bonds have a coupon higher than current market rates.

An issuer might call its bonds in extraordinary cases, including if:
  - it no longer needs the money for the original purpose;
  - the project is condemned or sold;
  - the project is destroyed and insurance proceeds are used to redeem the
    bonds;
  - any related credit support expires and is not replaced; or
  - interest on the bonds become taxable.

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

You can always sell back your units, but we cannot assure you that a liquid
trading market will always exist for the bonds in the portfolio, especially
since current law may restrict the Fund from selling bonds to any Sponsor. The
bonds will generally trade in the over-the-counter market. 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, it is said to
be "concentrated" in that bond type, which makes the Portfolio less diversified.

Here is what you should know about the Pennsylvania Portfolio'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 concentrations over time.

                                       8
<PAGE>
STATE CONCENTRATION RISK

PENNSYLVANIA RISKS

GENERALLY

Pennsylvania and many of its municipalities (including Philadelphia) have
undergone an economic decline:

  - coal, steel, railroads and other heavy industry historically associated with
    the Commonwealth has given way to increased competition from foreign
    producers.

  - agriculture and related industries are still an important part of the
    Commonwealth's economy.

  - recently, however, service sector industries (trade, medical and health
    services, education and financial services) have provided new sources of
    growth.

STATE AND LOCAL GOVERNMENTS

Historically, both the Commonwealth and the City of Philadelphia have
experienced serious revenue shortfalls. At the same time, rising demands for
state and local programs and services (particularly medical assistance and cash
assistance programs) have led to increased spending.

  - in recent years, both the Commonwealth and the City of Philadelphia have
    tried to balance their budgets with a mix of tax increases and spending
    cuts.

  - Philadelphia has considered significant service cuts and privatization of
    certain services which it has provided to date.

  - In 1991, the Commonwealth created the Pennsylvania Inter-Governmental
    Cooperation Authority ('PICA') which it authorized to issue debt to cover
    Philadelphia's budget shortfalls, eliminate the City's projected deficits
    and fund its capital spending. PICA issued approximately $1.76 billion of
    Special Revenue Bonds on Philadelphia's behalf. Its power to issue bonds on
    Philadelphia's behalf expired at the end of 1996; as of June 30, 1999,
    approximately $1.0 billion in PICA Special Revenue Bonds were outstanding.

  - Pennsylvania's general obligation bonds are currently rated Aa3 by Moody's
    and AA- by Standard & Poor's. Philadelphia's general obligation bonds are
    rated Baa2 by Moody's and BBB by Standard & Poor's. There can be no
    assurance that these ratings will not be lowered.

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

Some bonds are backed by insurance companies (as shown under 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.

                                       9
<PAGE>
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 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 the secondary market continuously for over 25 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

                                       10
<PAGE>
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 Defined Asset 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.

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 initial 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

                                       11
<PAGE>
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.

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; if
a contract to buy any 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.

                                       12
<PAGE>
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 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

                                       13
<PAGE>
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
counsel for the Sponsors, has given an opinion that the units are validly
issued. Special counsel located in the relevant states have given state and
local tax opinions.

AUDITORS

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

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 Bank of New York, 101 Barclay Street, 17 W, New York, New York 10268, 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 date of deposit of the bonds. Any cash
made available by you to the Sponsors before the settlement date

                                       14
<PAGE>
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

The Fund and the Agent for the Sponsors have each adopted a code of ethics
requiring reporting of personal securities transactions by its employees with
access to information on Fund transactions. Subject to certain conditions, the
codes permit employees to invest in Fund securities for their own accounts. The
codes are designed to prevent fraud, deception and misconduct against the Fund
and to provide reasonable standards of conduct. These codes are on file with the
Commission and you may obtain a copy by contacting the Commission at the address
listed on the back cover of this prospectus.

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"). To date we are not aware of any major operational difficulties
resulting from the computer system changes necessary to prepare for the Year
2000. However, there can be no assurance that the Year 2000 Problem will not
adversely affect the issuers of the bonds contained in the Portfolio. 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 minimum 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 issuers (or other users) have complied or will comply
with any requirements necessary

                                       15
<PAGE>
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 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 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,

                                       16
<PAGE>
your income from the Fund may be subject to state and local taxation. You should
consult your tax adviser in this regard.

PENNSYLVANIA TAXES

In the opinion of Drinker Biddle & Reath LLP, Philadelphia, Pennsylvania,
special counsel on Pennsylvania tax matters:

The Pennsylvania Trust will not be taxed as a corporation under the current
income tax laws of Pennsylvania. Your income from the Trust may be subject to
taxation depending on where you live. If you are a Pennsylvania taxpayer your
interest income from the Trust will be tax exempt to the extent that income is
earned on bonds that are tax exempt for Pennsylvania purposes. However, gains on
the sale of bonds by the Trust or on the sale of your Units will be subject to
Pennsylvania income tax. If you are a Philadelphia resident you may be subject
to the Philadelphia school district tax on any gains realized from the sale of
bonds by the Trust or the sale of Units by you to the extent either the bonds or
Units have been held for six months or less. You should consult your tax adviser
as to the consequences to you with respect to any investment you make in the
Trust.

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 portfolios, 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.

                                       17
<PAGE>

DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
PENNSYLVANIA SERIES - 12

REPORT OF INDEPENDENT ACCOUNTANTS

The Sponsors, Trustee and Holders
  of Defined Asset Funds - Municipal Investment Trust Fund,
  Pennsylvania Series - 12:

We have audited the accompanying statement of condition of Defined
Asset Funds - Municipal Investment Trust Fund, Pennsylvania
Series - 12, including the portfolio, as of January 31, 2000 and the
related statements of operations and of changes in net assets for the
years ended January 31, 2000, 1999 and 1998. 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 January
31, 2000, as shown in such portfolio, were confirmed to us by The
Bank of New York, 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, Pennsylvania
Series - 12 at January 31, 2000 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.
March 29, 2000


                                      D - 1
<PAGE>

DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
PENNSYLVANIA SERIES - 12

STATEMENT OF CONDITION
AS OF JANUARY 31, 2000

<TABLE>
<S>                                                <C>           <C>
TRUST PROPERTY:
  Investment in marketable securities - at value
    (cost $5,990,273)(Note 1)......................                  $6,421,087
  Receivable from security sold or redeemed........                      55,297
  Accrued interest receivable......................                      88,272
  Cash.............................................                      96,884
                                                                   _____________

              Total trust property.................                   6,661,540

LESS LIABILITIES:
  Redemptions payable..............................   $   55,511
  Accrued expenses.................................        5,524         61,035
                                                    _____________  _____________

NET ASSETS, REPRESENTED BY:
  10,534 units of fractional undivided
    interest outstanding (Note 3)..................    6,422,118
  Undistributed net investment income..............      178,387
                                                    _____________
                                                                     $6,600,505
                                                                   =============
UNIT VALUE ($6,600,505/10,534 units)...............                     $626.59
                                                                   =============

</TABLE>
                       See Notes to Financial Statements.


                                      D - 2
<PAGE>

DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
PENNSYLVANIA SERIES - 12

STATEMENTS OF OPERATIONS

<TABLE>
<CAPTION>
                                             .......Years Ended January 31,..........
                                                 2000         1999         1998
                                             _________________________________________
<S>                                        <C>          <C>          <C>
INVESTMENT INCOME:
  Interest income...........................    $381,483     $398,836     $419,300
  Trustee's fees and expenses...............     (14,786)     (13,067)     (16,897)
  Sponsors' fees............................      (2,036)      (1,099)          10
                                             _________________________________________
  Net investment income.....................     364,661      384,670      402,413
                                             _________________________________________

REALIZED AND UNREALIZED GAIN (LOSS)
  ON INVESTMENTS:
  Realized gain on securities sold
    or redeemed.............................      15,793       33,716       31,104
  Unrealized appreciation (depreciation)
    of investments..........................    (462,187)      48,815      219,056
                                             _________________________________________

  Net realized and unrealized gain (loss)
    on investments..........................    (446,394)      82,531      250,160
                                             _________________________________________

NET INCREASE (DECREASE) IN NET ASSETS
  RESULTING FROM OPERATIONS.................    $(81,733)    $467,201     $652,573
                                             =========================================

</TABLE>
                       See Notes to Financial Statements.


                                      D - 3
<PAGE>

DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
PENNSYLVANIA SERIES - 12

STATEMENTS OF CHANGES IN NET ASSETS

<TABLE>
<CAPTION>
                                               .......Years Ended January 31,..........
                                                   2000         1999         1998
                                               _________________________________________
<S>                                          <C>          <C>          <C>
OPERATIONS:
  Net investment income.......................  $  364,661   $  384,670   $  402,413
  Realized gain on securities sold
    or redeemed...............................      15,793       33,716       31,104
  Unrealized appreciation (depreciation)
    of investments............................    (462,187)      48,815      219,056
                                               _________________________________________
  Net increase (decrease) in net assets
    resulting from operations.................     (81,733)     467,201      652,573
                                               _________________________________________

DISTRIBUTIONS TO HOLDERS (Note 2):
  Income......................................    (366,648)    (384,431)    (409,846)
  Principal...................................     (71,811)     (80,167)     (47,259)
                                               _________________________________________
  Total distributions.........................    (438,459)    (464,598)    (457,105)
                                               _________________________________________
CAPITAL SHARE TRANSACTIONS - Redemptions of
  190, 498 and 532 units, respectively........    (122,023)    (335,416)    (352,017)
                                               _________________________________________
NET DECREASE IN NET ASSETS....................    (642,215)    (332,813)    (156,549)

NET ASSETS AT BEGINNING OF YEAR...............   7,242,720    7,575,533    7,732,082
                                               _________________________________________
NET ASSETS AT END OF YEAR.....................  $6,600,505   $7,242,720   $7,575,533
                                               =========================================
PER UNIT:
  Income distributions during year............      $34.41       $34.87       $35.72
                                               =========================================
  Principal distributions during year.........       $6.76        $7.32        $4.19
                                               =========================================
  Net asset value at end of year..............     $626.59      $675.37      $675.06
                                               =========================================
TRUST UNITS OUTSTANDING AT END OF YEAR........      10,534       10,724       11,222
                                               =========================================

</TABLE>
                       See Notes to Financial Statements.


                                      D - 4
<PAGE>

DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
PENNSYLVANIA SERIES - 12

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 10,534 units at Date of Deposit.............   $10,664,328
      Less sales charge...................................       399,869
                                                           ______________
      Net amount applicable to Holders....................    10,264,459
      Redemptions of units - net cost of 7,466 units
        redeemed less redemption amounts..................     1,573,738
      Realized loss on securities sold or redeemed........       (85,409)
      Principal distributions.............................    (5,761,484)
      Unrealized appreciation of investments..............       430,814
                                                           ______________

      Net capital applicable to Holders...................   $ 6,422,118
                                                           ==============
</TABLE>

  4.  INCOME TAXES

      As of January 31, 2000, unrealized appreciation of investments, based
      on cost for Federal income tax purposes, aggregated $430,814, all of
      which related to appreciated securities. The cost of investment
      securities for Federal income tax purposes was $5,990,273 at
      January 31, 2000.


                                      D - 5
<PAGE>

DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
PENNSYLVANIA SERIES - 12

PORTFOLIO
AS OF JANUARY 31, 2000

<TABLE>
<CAPTION>
                                         Rating                                       Optional
    Portfolio No. and Title of             of            Face                         Redemption
            Securities                   Issues(1)       Amount  Coupon Maturities(3) Provisions(3)          Cost      Value(2)
            __________                    _________       ______  ______ _____________ _____________          ____      ________
<S>                                      <C>       <C>           <C>       <C>        <C>            <C>           <C>
 1 Commonwealth of Pennsylvania,            AA        $  385,000   4.000%   2002       02/29/00         $  283,591    $  375,279
   General Obligation Bonds                                                            @ 100.750
                                                         315,000   4.000    2002       02/29/00            232,029       307,046
                                                                                       @ 100.750

 2 Pennsylvania Higher Educational          Aa2(m)       125,000   4.900    2008       02/29/00            107,500       120,753
   Facilities Authority, University of                                                 @ 100.000
   Pennsylvania Revenue Bonds, Ser. of
   1968

 3 Altoona Area School District             AAA        1,180,000   6.500    2008(5)    07/01/06          1,180,000     1,251,024
   Authority, Blair County,                                                            @ 100.000
   Pennsylvania, School Revenue Bonds
   Ser. of 1978

 4 Blackhawk School Building                AAA        1,270,000   6.375    2007       None              1,270,762     1,367,434
   Authority, Beaver County,
   Pennsylvania, School Building
   Revenue Refunding Bonds, Ser. of
   1978 (MBIA Ins.)(4)

 5 Exeter Township School Authority,        AAA          625,000   6.375    2001       None                625,375       644,863
   Berk County, Pennsylvania, School
   Revenue Bonds Ser. 1978 (MBIA
   Ins.)(4)

 6 Mount Lebanon High School                Aaa(m)       655,000   6.400    2000       None                655,000       655,609
   Authority, Allegheny County,
   Pennsylvania, School Building
   Revenue Refunding Bonds, Ser. of
   1978

 7 North Penn School Distric                Aaa(m)     1,050,000   6.200    2007       None              1,050,000     1,069,152
   Authority, Montgomery and Bucks
   Counties, Pennsylvania, School
   Revenue Bonds, Ser. of 1978
   (Refunding)

</TABLE>


                                      D - 6
<PAGE>

DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
PENNSYLVANIA SERIES - 12

PORTFOLIO
AS OF JANUARY 31, 2000

<TABLE>
<CAPTION>
                                         Rating                                       Optional
    Portfolio No. and Title of             of            Face                         Redemption
            Securities                   Issues(1)       Amount  Coupon Maturities(3) Provisions(3)          Cost      Value(2)
            __________                    _________       ______  ______ _____________ _____________          ____      ________
<S>                                      <C>       <C>           <C>       <C>        <C>            <C>           <C>
 8 Public Auditoriam Authority of           AAA       $   74,000   3.600%   2001       None             $   51,016    $   72,532
   Pittsburg and Allegheny County,
   Pennsylvania, Auditorium Bonds

 9 The Municipal Authority of the           NR           535,000   6.400    2017(5)    11/15/14            535,000       557,395
   Borough of West View Allegheny                                                      @ 100.000
   County, Pennsylvania, Water
   Revenue Bonds, Ser. of 1978
                                                    ______________                                    _____________ _____________
TOTAL                                                 $6,214,000                                        $5,990,273    $6,421,087
                                                    ==============                                    ============= =============
</TABLE>

                             See Notes to Portfolio.


                                      D - 7
<PAGE>

DEFINED ASSET FUNDS - MUNICIPAL INVESTMENT TRUST FUND,
PENNSYLVANIA SERIES - 12

NOTES TO PORTFOLIO
AS OF JANUARY 31, 2000

   (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) Insured by the indicated municipal bond insurance company.

   (5) Bonds with aggregate face amounts of $1,715,000 have been
       pre-refunded and are expected to be called for redemption on
       the optional redemption provision dates shown.


                                      D - 8


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DEFINED ASSET FUNDS--REGISTERED TRADEMARK--

<TABLE>
<S>                                      <C>
HAVE QUESTIONS ?                         MUNICIPAL INVESTMENT TRUST FUND
Request the most                         PENNSYLVANIA SERIES--12
recent free Information                  (A Unit Investment Trust)
Supplement that gives more               ---------------------------------------
details about the Fund,                  This Prospectus does not contain
by calling:                              complete information about the
The Bank of New York                     investment company filed with the
1-800-221-7771                           Securities and Exchange Commission in
                                         Washington, D.C. under the:
                                         - Securities Act of 1933 (file no.
                                         2-60147) 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.
                                                                     12770--4/00
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