We performed SEREX (serological identification of antigens by recombinant cDNA expression cloning) using the sera of patients with esophageal squamous cell carcinoma (SCC), and examined whether some of the SEREX antigens can affect chemosensitivity against anticancer drugs. We isolated a novel gene which was designated as AISEC (antigen identified by SEREX for esophageal carcinoma). RT-PCR analysis showed that the mRNA expression levels of AISEC were higher in esophageal SCC tissues than in their normal counterparts. By transfection into activated Ha-ras-transformed NIH3T3 (ras-NIH) mouse fibroblasts, we isolated a clone, FAISEC-3, which stably expressed AISEC. FAISEC-3 cells were more resistant to anticancer drugs, such as mitomycin C, ifosfamide, vincristine, camptothecin and etoposide, than parental ras-NIH cells. Luciferase reporter assay after a transient transfection with AISEC cDNA or the control vector revealed that the transactivity of p53 was suppressed by AISEC in a dose-dependent manner. These results suggested that esophageal SCC tissues produce AISEC in increased amounts, which can reduce the chemosensitivity against anticancer drugs possibly by suppressing the p53 transactivation ability.