The anticancer agent neocarzinostatin (NCS) was bound covalently to human/mouse chimeric Fab fragments of the monoclonal antibody A7 to form the conjugate chA7Fab-NCS. The antitumor effect of chA7Fab-NCS was tested by measuring the inhibition of 3H-thymidine incorporation into human pancreatic carcinoma cells. The chA7Fab-NCS was approximately 2.3 times as effective as free NCS against human pancreatic carcinoma cells which reacted with the monoclonal antibody A7. The antitumor activity of chA7Fab-NCS was inhibited by excess chA7Fab. ChA7Fab-NCS had an antitumor effect equivalent to free NCS on human pancreatic carcinoma cells which did not react with the monoclonal antibody A7. ChA7Fab-NCS appears to be a potentially useful conjugate for immunotargeting chemotherapy against pancreatic carcinoma.