A randomized two-stage, phase II study was conducted to assess the antitumor activity of two different schedules of topotecan in the treatment of extensive-stage small-cell lung cancer (SCLC) in chemotherapy-naive patients. A total of 40 eligible patients were randomized to receive either the daily schedule, with topotecan being administered intravenously at 1.5 mg/m2 daily for 5 days every 3 weeks, or the continuous-infusion schedule, with topotecan administered intravenously at a dosage of 1.3 mg/m2 per day over 72 hours every 4 weeks. Randomization to the continuous-infusion schedule was discontinued due to inactivity, and an additional 20 patients were treated on the daily schedule. Patients received an average of 5 courses (range: 1-13) of the daily schedule compared to an average of 2 courses (range: 1-7) of the continuous-infusion schedule (p < 0.01). Confirmed response rates for the daily and continuous-infusion schedules are 62.5% (90% CI: 49-75%) and 15% (90% CI: 1-29%), respectively. Toxicity was predominantly hematologic with 92% (55/60) having greater than or equal to grade III neutropenia and 58% (35/60) reporting greater than or equal to grade III leukopenia for both IV schedules. Nonhematologic toxicity was very mild, with only 10% (6/60) patients experiencing grade IV toxicities. One patient died of infection on the continuous-infusion arm. Median times to progression for the daily and continuous-infusion schedules are 5 months (90% CI: 4.4-7.2) and 2 months (90% CI: 1.1-2.1), respectively. Estimated 1-year survival rates for patients receiving daily and continuous-infusion schedules are 63% (90% CI: 51-76%) and 55% (90% CI: 39-77%), respectively. Fifty percent (30/60) of patients received second-line therapy with etoposide and cisplatin. Forty-three percent (13/30) of patients who received second-line therapy achieved a confirmed response. Topotecan showed significant activity in the treatment of extensive stage SCLC when administered as a brief daily IV repeated every 3 weeks.