By means of nuclide precursor incorporation, the effects of 211At labelled monoclonal antibody against gastric cancer (211At-3H11McAb) on DNA, RNA and protein synthesis in gastric cancer cell were studied. The results show that 211At-3H11McAb and Na211At-3 inhibit 3H-TdR, 3H-UR and 3H-Leu incorporation, especially 3H-UR incorporation, into gastric cancer cell at 3.7 x 10(4)Bq and 1.85 x 10(5)Bq; the inhibiting rates depend on concentration. The DNA biosynthesis in gastric cancer cell gradually recover after the drug is removed, suggesting that the drug should exert an inhibiting action on DNA biosynthesis in tumor cell through interference of DNA metabolism.