CPT-11 is a derivative of camptothecin, a topoisomerase-I inhibitor with marked cytotoxic activity. We examined the cytotoxicity of CPT-11 and its metabolite SN-38 for primary gastrointestinal carcinoma and various recurrent carcinomas which were cultured on contact-sensitive plates (CSPs). The response rate of seven gastrointestinal carcinomas for either CPT-11 or SN-38 was 71% (5/7). The response was higher than those for other anticancer agents, including adriamycin (ADM), cisplatinum (CDDP) and 5-fluorouracil (5-FU). The mean percent survival of these tumor cells was 69% when incubated with 25 ng/ml of SN-38, which was the lowest survival for all the anticancer drugs tested. IN the case of recurrent carcinomas, the response rate to either CPT-11 or SN-38 was 60% (3/5), and was higher than the rates for MMC, CDDP or 5-FU. The mean percent survival of the recurrent carcinoma cells was 76% in the presence of 25 ng/ml SN-38, and this was once again the lowest survival rate. CPT-11 had a stronger inhibitory effect against one carcinoma than SN-38 when a clinical drug concentration was added to the culture medium, suggesting that CPT-11 itself was cytotoxic. IN addition, one carcinoma with a low response to CDDP also showed no response to CPT-11, but was very occurred because of decreased conversion of CPT-11 to SN-38. Our results suggest that CPT-11 may be a useful agent for the treatment of both primary gastrointestinal cancer and various recurrent carcinomas.