Patients with limited stage small cell lung cancer were initially randomized to receive either three courses of Cyclophosphamide, Adriamycin, and Vincristine (CAV) followed by three courses of VP-16 and Cis-platin (VP-PT) or six courses of alternating CAV and VP-PT. Responding patients received prophylactic cranial radiation (PCI) after three courses of chemotherapy (CT) and loco-regional thoracic radiation (LRTR) after six courses. No maintenance chemotherapy was given. Patients receiving LRTR were randomized to receive either 25 Gy in ten fractions over 2 weeks (SD) or 37.5 Gy in 15 fractions over 3 weeks (HD). In both arms the pre-chemotherapy disease was treated with a 2 cm margin around the primary tumor volume. The mediastinum was included in the treatment volume and the supraclavicular nodes were also included if involved originally. The spinal cord was shielded after 32 Gy. Of the 333 patients enrolled by the time the trial closed in October 1984, 168 were eventually randomized to LRTR and are eligible for response assessment. The overall response rate after combined RT and CT was 94% (CR 67%, PR 27%). The CR rate for SD was 65% and for HD 69%. The combined treatment was well tolerated by most patients. Forty-nine percent of HD patients developed dysphagia compared to 26% of those SD (p less than 0.01). At the time of this analysis the median duration of follow-up since randomization to radiotherapy is 30 months. The median local progression-free survival on HD is 49 weeks. On SD it is 38 weeks (p = 0.05, one sided). The actuarial incidence of local progression by 2 years is 69% on HD and 80% on LD. There is as yet no significant difference in overall survival between the two arms. It appears that HD radiotherapy as administered in this study may have an impact on local control, but it is too early to determine if this will translate into a survival benefit.