This randomized phase II multi-center study was designed to determine the time to progression, duration of response and the feasibility of an intensified maintenance regime consisting of a combination of interferon (IFN)-alpha and retinoic acid after high-dose combination chemotherapy and radiotherapy in patients with small cell lung cancer. The patients received four courses of combination chemotherapy consisting of ifosfamide, carboplatin and etoposide, with higher doses of ifosfamide and carboplatin given in the first course, with routine growth factor support. Responding patients were then randomly assigned to one of three maintenance therapy arms. All patients with limited disease (LD) were given thoracic radiotherapy before maintenance therapy and those who had also achieved a complete response (CR) or minimal residual disease (MRD) received prophylactic cranial irradiation. In Arm 1 patients received IFN-alpha-2a, 6 MIU s.c. TIW for 4 weeks, followed by 3 MIU s.c. TIW, and 13-cis-retinoic acid 1 mg/kg/day p.o. BID daily. In Arm 2 patients received trophosphamide 100-150 mg/day p.o. BID. No maintenance treatment was given in Arm 3, the control group. Maintenance therapy was continued for 1 year. Eighty-five patients were treated according to the protocol. Twenty-one patients achieved CR, four achieved MRD and forty-two achieved partial responses to chemotherapy and radiotherapy. Sixty patients (71%) were randomly assigned for maintenance treatment. Median survival was 17.1 months in the IFN-alpha-retinoic acid arm, 12.4 months in the trophosphamide arm and 13.5 months in the control arm. One-year survival rates were 82, 56 and 55%, respectively. Duration of response was 6.5, 5.5 and 4.7 months, respectively. Time to progression was 8.6, 8.0 and 6.8 months, respectively The differences were not statistically significant. The IFN-alpha-retinoic acid maintenance treatment was well tolerated. Patients who received IFN-alpha-retinoid maintenance therapy lived longer after the onset of progressive disease. The treatment regime was effective, feasible and well tolerated.