Thirty-two patients (27, extensive disease; five, regional disease) with histologically documented small cell carcinoma entered a randomized study to determine the efficacy of intensive induction chemotherapy. The necessity of a protected environment (laminar air flow room) during this treatment was also evaluated. Patients received high-dose or standard-dose cyclophosphamide, methotrexate, and CCNU (CMC) during the first 6 weeks of treatment. Subsequent maintenance therapy consisted of standard-dose CMC until disease progression. In 23 patients treated with high-dose chemotherapy there were responses in 96% (30% complete). Standard-dose chemotherapy gave responses in 45%, none of which were complete. Median survival correlated with completeness of response and was 16+ months for the seven complete responders. Patients receiving high-dose CMC spent an average of 10 days with neutrophil counts less than 1000/mm3. There was only one documented, non-fatal infection. High-dose chemotherapy gives better responses and longer survival than previously utilized standard doses of the same drugs. Patients could safely be treated in the hospital ward.