In order to assess the effectiveness of chest irradiation in addition to intensive chemotherapy in the treatment of limited stage small cell lung cancer, 56 patients were randomized to receive either chemotherapy alone or chemotherapy plus chest irradiation, between April 1981 and September 1986. The chemotherapy regimen consisted of a four-drug combination of cyclophosphamide, vincristine, methotrexate and procarbazine, and a three-drug combination of VP-16, adriamycin and nimustine, given alternately every 8 weeks. One group of 28 patients received chemotherapy alone, and another group of 28 patients received chest irradiation of 40Gy, in 20 fractions over 4 weeks, between cycles 1 and 2 of the chemotherapy. Complete response rate were similar in the two groups; 46% for those receiving chemotherapy alone, and 62% for those receiving chemotherapy plus chest irradiation. There was no significant difference in the median survival time (14.5 months for chemotherapy alone versus 12.0 months for chemotherapy plus chest irradiation). The combined modality treatment was more toxic than chemotherapy alone; two patients receiving such treatment died of radiation pneumonitis. However, as far as the 3-year survival rate, there was a trend favoring patients receiving the combined modality treatment (11% versus 19%). Although additional studies are required to determine the optimal dose and schedule, timing, and selection of patients as for chest irradiation, the major need for the treatment of small cell lung cancer is better systemic chemotherapy. It seems likely that the role of chest irradiation will become more important as improved chemotherapy is developed.