The effects of 2 route chemotherapy using cis-diamminedichloroplatinum-(II) (DDP) and its antidote sodium thiosulfate (STS), given i.p. and s.c., respectively, were assessed in peritoneally disseminated cancer in rats. Administration of STS s.c. to mice 1 min before DDP i.p. was most effective in protecting the animals against the lethal toxicity of DDP. The LD50 values of DDP i.p. with and without STS were .apprx. 55 mg/kg and 14 mg/kg, respectively. This 2 route chemotherapy using DDP and STS was significantly superior in therapeutic efficacy to single treatment with DDP.