A multi-institutional collaborative late phase II study of irinotecan hydrochloride (CPT-11) was performed on patients with advanced gastric cancer. CPT-11 was administered as a 100 mg/m2 weekly intravenous infusion or as 150 mg/m2 fortnightly. Of 81 registered patients, 77 cases were eligible and 60 cases were evaluable for response. The overall response rate for evaluable cases was 23.3% (14/60), and the response rate was 16.1% (9/45) for the patients who had received prior chemotherapy. The primary tumor showed a 4.5% response, while metastatic lesions in the lymph-nodes, lungs, and liver showed response rates of 36.4%, 33.3%, and 17.4%, respectively. The major toxicities (> or = Grade 3) were leukopenia (41.2%), anemia (28.9%), diarrhea (22.4%) and anorexia (19.7%). These toxicities were generally reversible. CPT-11 showed activity against advanced gastric cancer, suggesting that further clinical studies of CPT-11 combined with other active chemotherapy agents are warranted.