Forty-five patients with advanced, measurable, or evaluable non-small bronchogenic carcinoma (NSCBC) were treated with doxorubicin and mitomycin C combination chemotherapy. The first 27 patients received doxorubicin 50 mg/m2 I.V. every 3 weeks and mitomycin C 10 mg/m2 I.V. every 3 weeks. Because of severe cardiopulmonary toxicity in seven patients, with four otherwise unexplained deaths, the next 18 patients were treated with the mitomycin C dose reduced to 10 mg/m2 every 6 weeks. Overall, 11 patients (25%) responded, with one complete and 10 partial remissions. Eight responses (30%) were observed in the patients who received mitomycin C every 3 weeks and three responses (17%) were found in those given mitomycin C every 6 weeks (p less than 0.5), with no cardiopulmonary toxicity in the latter group. The median survival was 21 weeks for the entire group of patients, with the group receiving mitomycin C every 3 weeks living a median of 15.5 weeks and those given mitomycin C every 6 weeks surviving 35.5 weeks (p less than 0.025). We conclude that there is a higher tumor response rate but more cardiopulmonary toxicity and shorter survival among the group receiving mitomycin C every 3 weeks compared to those receiving mitomycin C every 6 weeks. Future studies should consider this toxicity of mitomycin C administered on an every-3-week schedule.