The effect of pretreatment with bismuth subnitrate (BSN) for prevention of the renal toxicity of cisplatin (CDDP) was examined in 44 patients with lung cancer (43 non-small cell and one small cell lung cancer). In non-small cell lung cancer cases, the effect of the antitumor activity of chemotherapeutic drugs was observed in 62% of patients pretreated with BSN, and 42% in the group without pretreatment with BSN. No antitumoral activity of chemotherapeutic drugs was suppressed by treatment with BSN. In the group without pretreatment of BSN, serum creatinine and BUN were in proportion to the number of administrations of chemotherapeutic drugs. On the other hand, no renal toxicity was shown in the group with pretreatment by BSN. No protective effect against myelosuppression with pretreatment by BSN was demonstrated, perhaps because of the influence of anti-cancer drugs apart from CDDP.