A dose-escalation study was conducted for postoperative patients with stage IV gastric cancer to determine the recommended dose of daily intravenous cisplatin combined with a fixed dose of TS-1. TS-1 was administered orally twice daily for 2 weeks followed by a 1-week rest. The dose of TS-1 was based on the body surface area (BSA) as follows: 80 mg/day for BSA less than 1.25, 100 mg/day for BSA 1.25 to less than 1.50, and 120 mg/day for BSA 1.5 or more. Three dose levels of cisplatin (2, 4, 6 mg/m(2)) were studied, and two courses were performed. Cisplatin was infused on day 1-5 and 8-12 for 30 minutes. The National Cancer Institute common toxicity criteria (NCI-CTC Version 3) were used to evaluate the grade of toxicity. Three patients enrolled in each level. Dose escalation was performed when dose-limiting toxicities (DLT) were seen in 0/3, and 3 more cases of the same level were added when DLTs were seen 1-2/3. Maximum-tolerated dose (MTD) were determined when DLTs were seen in 3 cases. DLTs were not recorded during the administration of CDDP up to 4 mg/m(2). However, DLTs were seen 3/3 at level 3. From these results, cisplatin of 4 mg/m(2)was determined to be the recommended dose (RD) in this protocol for postoperative stage IV gastric carcinoma.