We reported the results of phase I study with CPT-11 and S-1 (IRIS) in advanced gastric cancer (AGC) patients at ASCO 2002. Now I present an outline of this phase I/II trial. A combined treatment of IRIS (CPT-11 + S-1) was given to the AGC patients who had not received prior chemotherapy. S-1 was orally administered twice a day for 14 days, and CPT-11 was administered as a 90-minute intravenous infusion on days 1 and 15. This schedule was repeated every 4 weeks. Fifteen patients were registered in this phase I study and 9 patients were added in this phase II study. Non-hematological toxicities were almost classified as grade 2 or lower, except for grade 3 nausea and grade 3 dermatitis of level 2. These adverse events were manageable by administering anti-emetic drugs and a drug rest. As for hematological toxicities, grade 4 neutropenia occurred with one patient at level 1 and level 2 in phase I. And grade 4 neutropenia occurred with four patients at level 2 in phase II. However, they recovered after the drug rest, and we could continue the administration based on the standard dose modifications. These side effects were tolerable, and the overall response rate was 54.2%. MST of this regimen is 581 days. The IRIS treatment is effective and tolerable for outpatient treatments.