Techniques which can increase the expression level of tumor-associated antigens may improve immunotargeting therapy. We studied the reactivity of MAb A7 toward an antigen expressed on the surface of the human pancreatic cancer cell line HPC-YS after treatment with various antitumoral agents. When we applied 1 microg/ml mitomycin C (MMC) or 0.1 microg/ml neocarzinostatin (NCS) for 1 h, A7 recognizing antigen expression was enhanced until 24 h after the treatments. At a dose that completely suppressed cell growth, increased antigen expression was maintained for 96 h. Therefore, this study suggests that the combined application of an anticancer drug and MAb A7 may be useful for immunotargeting chemotherapy.