<TABLE> <S> <C>
<PAGE>
<ARTICLE> 5
<LEGEND>
THE FINANCIAL DATA SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED
FROM TANOX'S 10-Q FOR THE NINE MONTHS ENDED SEPTEMBER 30, 2000 AND IS QUALIFIED
IN ITS ENTIRETY BY REFERENCE TO SUCH MATTERS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> 9-MOS
<FISCAL-YEAR-END> DEC-31-2000
<PERIOD-START> JAN-01-2000
<PERIOD-END> SEP-30-2000
<CASH> 39,998
<SECURITIES> 235,952
<RECEIVABLES> 5,448
<ALLOWANCES> 0
<INVENTORY> 0
<CURRENT-ASSETS> 194,138
<PP&E> 12,735
<DEPRECIATION> (5,402)
<TOTAL-ASSETS> 286,538
<CURRENT-LIABILITIES> 6,889
<BONDS> 0
0
0
<COMMON> 426
<OTHER-SE> 269,223
<TOTAL-LIABILITY-AND-EQUITY> 286,538
<SALES> 0
<TOTAL-REVENUES> 12,464
<CGS> 0
<TOTAL-COSTS> 0
<OTHER-EXPENSES> 17,914
<LOSS-PROVISION> 0
<INTEREST-EXPENSE> 628
<INCOME-PRETAX> 2,800
<INCOME-TAX> (2,057)
<INCOME-CONTINUING> 743
<DISCONTINUED> 0
<EXTRAORDINARY> 0
<CHANGES> 0
<NET-INCOME> 743
<EPS-BASIC> 0.02
<EPS-DILUTED> 0.02
</TABLE>