Fifteen patients with advanced renal-cell carcinoma were treated with the combination of mitomycin-C 14-20 mg/m2 i.v. every 7 weeks and metronidazole 1,500 mg/m2 p.o. 12 and 1 h before and 6 and 24 h after the mitomycin-C. Of 12 patients evaluable for response, three (25%) responded with partial remissions. Myelosuppression did not appear to be increased over that seen with mitomycin-C alone. Pulmonary toxicity occurred in three patients and was fatal in two. The incidence of pulmonary toxicity was probably increased over that seen with mitomycin-C alone. Renal toxicity was also seen. Based on this small study, it was our feeling that this dose-schedule of metronidazole did not appear to result in enough of an augmentation of the efficacy of mitomycin-C against renal-cell carcinoma to justify the incidence of serious toxicity.