<PAGE>
Supplement to Prospectus
Nuveen Tax-Exempt Unit Trust
Breakpoint Sticker
April 13, 1994
The Sponsor has increased the number of breakpoints at which investors
can enjoy sales charge reductions for primary market volume purchases
and has provided for the establishment of letters of intent by Unitholders
to permit such Unitholders to receive a reduced sales charge based on the
aggregate intended amount expressed in the letter of intent. New
breakpoints have been added for purchases in excess of $50,000,
$2,500,000 and $5,000,000. Accordingly, notwithstanding anything to
the contrary in this Prospectus, the sales charge applicable to quantity
purchases is reduced on a graduated scale for sales to any purchaser of at
least $50,000 or 500 Units and will be applied on whichever basis is
more favorable to the purchaser. For purposes of calculating the
applicable sales charge, purchasers who have indicated their intent to
purchase a specified amount of Units of the Trust described herein in the
primary offering period or units of any other series of Nuveen Tax-
Exempt Unit Trusts in the primary offering period by executing and
delivering a letter of intent to the Sponsor, which letter of intent must be
in a form acceptable to the Sponsor and shall have a maximum duration
of thirteen months, will be eligible to receive a reduced sales charge
according to the following table based on the amount of intended
aggregate purchases as expressed in the letter of intent. By establishing
a letter of intent, a Unitholder agrees that the first purchase of Units
following the execution of such letter of intent will be at least 5% of the
total amount of the intended aggregate purchases expressed in such
Unitholder's letter of intent. Further, through the establishment of the
letter of intent, such Unitholder agrees that Units representing 5% of the
total amount of the intended purchases will be held in escrow by United
States Trust Company of New York pending completion of these
purchases. All distributions of Units held in escrow will be credited to
such Unitholder's account. If total purchases prior to the expiration of
the letter of intent period equal or exceed the amount specified in a
Unitholder's letter of intent, the Units held in escrow will be transferred
to such Unitholder's account. If the total purchases are less than the
amount specified, the Unitholder involved must pay the Sponsor an
amount equal to the difference between the amounts paid for these
purchases and the amounts which would have been paid if the higher
sales charge had been applied. If such Unitholder does not pay the
additional amount within 20 days after written request by the Sponsor or
the Unitholder's securities representative, the Sponsor will instruct the
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Trustee to redeem an appropriate number of the escrowed Units to meet
the required payment. By establishing a letter of intent, a Unitholder
irrevocably appoints the Sponsor as attorney to give instructions to
redeem any or all of such Unitholder's escrowed Units, with full power
of substitution in the premises. A Unitholder or his securities
representative must notify the Sponsor whenever such Unitholder makes
a purchase of Units that he wishes to be counted towards the intended
amount. Sales charges during the primary offering period are as
follows:
<TABLE>
National and State Long Intermediate Intermediate
Trusts Trusts Trusts
Percent Percent Percent Percent Percent Percent
of of Net of of Net of of Net
Number of Offering Amount Offering Amount Offering Amount
Units* Price Invested Price Invested Price Invested
__________________________________________________________________________________________________________________
<S> <C> <C> <C> <C> <C> <C>
Less than 500 4.90% 5.152% 4.25% 4.439% 3.90% 4.058%
500 but less than 1,000 4.75 4.987 4.15 4.330 3.70 3.842
1,000 but less than 2,500 4.50 4.712 3.85 4.004 3.50 3.627
2,500 but less than 5,000 4.25 4.439 3.60 3.734 3.25 3.359
5,000 but less than 10,000 3.50 3.627 3.35 3.466 3.00 3.093
10.000 but less than 25,000 3.00 3.093 3.00 3.093 2.75 2.828
25,000 but less than 50,000 2.50 2.564 2.50 2.564 2.50 2.564
50,000 or more 2.00 2.041 2.00 2.041 2.00 2.041
---------------------------------
Short Intermediate
Trusts Short Term Trusts
Percent Percent Percent Percent
of of Net of of Net
Offering Amount Offering Amount
Number of Units* Price Invested Price Invested
Less than 500 3.00% 3.093% 2.50% 2.564%
500 but less than 1,000 2.80 2.881 2.30 2.354
1,000 but less than 2,500 2.60 2.670 2.10 2.145
2,500 but less than 5,000 2.35 2.407 1.85 1.885
5,000 but less than 10,000 2.10 2.145 1.60 1.626
10,000 but less than 25,000 1.85 1.885 1.35 1.368
25,000 but less than 50,000 1.80 1.833 1.25 1.266
50,000 or more 1.50 1.523 1.15 1.163
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*Breakpoint sales charges are computed both on a dollar basis and on the basis of the
number of Units purchased, using the equivalent of 500 Units to $50,000, 2,500 Units
to $250,000, etc., and will be applied on that basis which is more favorable to the
purchaser.
</TABLE>
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In addition, the schedule for determining the amount of dealer
concessions on primary market purchases of Trust Units has been
modified in response to the increase in available breakpoints.
Accordingly, notwithstanding anything to the contrary in this Prospectus,
the Sponsor plans to allow a discount to brokers and dealers in
connection with the primary distribution of Units. The primary market
discounts are as follows:
<TABLE>
Discount per Unit
Long Inter- Inter- Short Inter-
Natl. and mediate mediate mediate Short Term
State Trusts Trusts Trusts Trusts Trusts
Number of Units*
____________________________________________________________________________________________________________
<S> <C> <C> <C> <C> <C>
Less than 500 $3.20 $2.90 $2.70 $2.00 $1.50
500 but less than 1,000 3.20 2.90 2.70 2.00 1.50
1,000 but less than 2,500 3.20 2.70 2.50 1.80 1.30
2,500 but less than 5,000 3.20 2.45 2.25 1.55 1.05
5,000 but less than 10,000 2.50 2.45 2.25 1.55 1.05
10,000 but less than 25,000 2.00 2.00 2.00 1.30 .80
25,000 but less than 50,000 1.75 1.75 1.75 1.30 .60
50,000 or more 1.75 1.50 1.50 1.00 .60
*Breakpoint sales charges and related dealer concessions are computed both on a dollar basis and
on the basis of the number of Units purchased, using the equivalent of 500 Units to $50,000,
2,500 Units to $250,000, etc., and will be applied on that basis which is more favorable to
the purchaser.
</TABLE>
The Sponsor reserves the right to change the foregoing dealer
concessions from time to time.
Nuveen Tax-Exempt Unit Trust, Series 721
RULE 497(d)
SEC FILE NO. 33-52321
April 15, 1994
This is the first page of the Prospectus Supplement dated April 15,
1994 of the Prospectus for the above named series.
