Seventeen previously untreated patients with metastatic non-small-cell lung cancer were entered in this phase I trial. Treatment consisted of a combination of acivicin and cisplatin at a starting dose of 12 and 15 mg/m2, respectively, given i.v. during 5 days and repeated every 28 days. A total of 46 cycles was given. Renal function abnormality was the dose-limiting toxicity of cisplatin with a maximum tolerated dose of 12 mg/m2. This toxicity occurred at a dose lower than expected, indicating a possible potentiation of platinum renal toxicity by acivicin. Myelosuppression was the dose-limiting toxicity of acivicin, with a maximum tolerated dose of 12 mg/m2. Other side effects included generalized weakness and gastrointestinal and neurological symptoms. In 15 patients evaluable for response seven progressed, six were stable for a median duration of 13 weeks, and two patients achieved a partial remission lasting 8 and 24 weeks, respectively. The overall response rate was 13%. The recommended phase II dose of both agents in this schedule was 12 mg/m2. The possible enhancement of cisplatin toxicity might have compromised the overall response rate of the combination and further studies using these drugs in this schedule are not recommended.