Based on experimental observations that verapamil and tamoxifen reverse multiple drug resistance, the authors investigated the feasibility of combining both agents with the initial chemotherapy of extensive small cell lung cancer. Overall, in a consecutive series of 58 patients the most important toxicity was myelosuppression, and there was a 24% rate of severe infections. Therapeutic results included 24% complete and 34% partial response rates, median time to disease progression of 32 weeks, and median survival of 46 weeks. In three consecutive cohorts of patients the dose of either tamoxifen or verapamil were escalated by 25% and 33%, respectively. The cohort of patients receiving verapamil 360 mg/day and tamoxifen 100 mg/day (level 2) had slightly more toxicity but also more responses than the other groups. Therefore, the authors recommend that these doses be used in controlled trials to confirm the promising results of their study.