A phase II clinical study of 254-S, a new anticancer platinum complex for gastrointestinal cancers, was conducted by the 254-S Gastrointestinal Cancer Study Group consisting of 16 institutions. 254-S was administered at 100 mg/m2 by intravenous drip infusion. This administration was repeated at 4-week intervals. The cases in which 254-S could be administered at least two times were regarded as complete cases evaluable for tumor response; of 75 cases registered, 53 were complete cases (29 cases with esophageal cancer, 12 with stomach cancer and 12 with colon cancer). As a result, 15 partial responses (PR) were obtained in the 29 patients with esophageal cancer and 1 PR from the 12 patients with stomach cancer, for a 51.7% and 8.3% response rate, respectively. 5 PR (55.6%) were obtained in 9 esophageal cancer patients with prior chemotherapy, including 2 PR in 4 patients previously treated with cisplatin. Major toxic effects observed were hematotoxicity including thrombocytopenia (59.0%), leukopenia (68.9%) and anemia (57.4%) and gastrointestinal toxicity such as nausea and vomiting (63.9%) and anorexia (41.0%); since grade 3 or 4 thrombocytopenia was observed with an incidence of 27.9%, careful monitoring seems to be required during the treatment with this product. Abnormal parameter changes on renal function included elevations of BUN (18.0%) and serum creatinine (9.8%). Based on these results, it was concluded that 254-S is a useful anticancer agent for the treatment of esophageal cancer.