A continuous hyperthermic peritoneal perfusion using high-dose cis-diamminedichloroplatinum (CDDP) and its antidote, sodium thiosulfate, was applied to eight patients with peritoneal metastasis from gastric cancers. Two of eight patients showed partial response and the rate of decrease of ascites was 38%. Renal failure and leukopenia were observed in one and two patients, respectively, but no severe or lethal dysfunction was observed and all were tolerated. These results showed that CDDP exerted anti-tumor effects on peritoneal metastasis from gastric cancers when used in high doses in combination with hyperthermia.