The participation of renal metallothionein (MT) in the toxicity and antitumor activity of cis-diamminedichloroplatinum(II) (cis-DDP) in male mice was examined. Preinduction of MT in the kidney by the s.c. administration of bismuth compounds decreased the lethality and renal and gastrointestinal toxicity caused by a single s.c. injection of cis-DDP. In the present study a correlation between the protective effect of pretreatment with bismuth nitrate against cis-DDP toxicity and the preinduced MT levels in the kidney was observed. Bismuth nitrate pretreatment showed no effect on the antitumor activity of cis-DDP against several transplantable tumors, probably because it induces MT in the kidney but not in tumor tissues. The fact that p.o. preadministration of bismuth subnitrate, an antidiarrheal drug, also depressed the lethal toxicity of cis-DDP is promising for its prompt application in medical attention. Thus, bismuth pretreatment allows higher doses of cis-DDP with no apparent toxicity, resulting in more efficient utilization of this anticancer drug.