Mitomycin-C was evaluated in a disease-oriented phase II trial in patients with small cell lung cancer who had failed prior conventional chemotherapy. The drug was given as a direct i.v. injection of 15 mg/m2 repeated every 6 weeks. No objective tumor response was observed among 15 evaluable patients. This precludes a 20% level of activity with 95% confidence. Leukopenia (60% of patients) and thrombocytopenia (20% of patients) were common-effects observed. One patient developed a microangiopathic hemolytic anemia after a total mitomycin-C dose of 42 mg. We conclude that mitomycin-C in this dose and schedule is an inactive agent in previously treated patients with small cell lung cancer.