One hundred eighty-six patients with advanced non-small-cell lung cancer were randomly assigned to treatment with combined 5-fluorouracil, doxorubicin, and mitomycin C (FAM) or combined methotrexate, doxorubicin, cyclophosphamide, and lomustine (MACC). Respective objective regression rates were comparable at 20% and 16%. Distribution of intervals to progression (overall median, 2.8 months) and survival times (overall median, 5.0 months) were essentially identical between the two regimens. The comparability of therapeutic effect was also evident within the subset of 81 patients who had adenocarcinoma cell type, although MACC showed a small advantage in survival after covariate analysis. In large-cell carcinoma, MACC showed a higher regression rate than that of FAM as well as a small advantage in survival. In squamous-cell carcinoma, however, FAM was superior to MACC in regression rates (32% v 4%) and also provided somewhat longer survival. With regard to toxicity, MACC produced a higher incidence of nausea and vomiting, whereas FAM produced more frequent and severe thrombocytopenia. From an overall standpoint, the therapeutic accomplishments of both regimens were disappointing. Our study does, however, provide additional evidence that mitomycin C-containing regimens may be selectively effective for squamous-cell carcinoma of the lung.