In order to investigate the efficacy of the intra-tumoural administration of an anticancer drug-monoclonal antibody conjugate in athymic nude mice bearing xenografts of a human pancreatic carcinoma, we examined the clearance of the murine monoclonal antibody A7 from the xenografts after intravenous or intra-tumoural administration and measured the antitumour effect of neocarzinostatin conjugated to MAb A7 following intravenous or intra-tumoural injection. Compared with 125I-labelled normal mouse IgG, a larger amount of 125I-labelled A7 remained in the tumour after both intravenous and intra-tumoural injection, and a significantly larger amount of 125I-labelled A7 remained in the tumour after intra-tumoural injection than that after intravenous injection. Moreover, a larger amount of 125I-labelled A7-NCS localized in the tumour after intra-tumoural injection than that after intravenous injection. Neocarzinostatin conjugated to MAb A7 showed greater activity against human pancreatic cancer than neocarzinostatin alone after both intravenous and intra-tumoural administration. Tumour growth was suppressed completely by the intra-tumoural administration of A7-NCS at a dose that did not suppress tumour growth via the intravenous route. These observations suggest that the intra-tumoural injection of neocarzinostatin conjugated to MAb A7 offers promise in treating pancreatic carcinoma.