In this study, we conjugated chimeric Fab fragments of the monoclonal antibody (MAb) A7, which reacts with pancreatic cancers, to the antitumor drug neocarzinostatin (chA7Fab-NCS) and intravenously injected 125I-labeled chA7Fab-NCS into nude mice bearing a human pancreatic cancer xenograft. We compared the tumor localization of 125I-labeled chA7Fab-NCS with that of conventional 125I-labeled A7-NCS, which was produced by conjugation of MAb A7 and NCS. 125I-Labeled chA7Fab-NCS accumulated in the tumor earlier than 125I-labeled A7-NCS, and significantly larger amounts of 125I-labeled chA7Fab-NCS had accumulated in the tumor 1 hour after injection. The results suggest that chA7Fab may be a suitable carrier for NCS in immunotargeting therapy against pancreatic cancer.