Three hundred and four cases of small cell lung cancer diagnosed histologically were included in a randomised multi-centre trial (23 centres) from 1st January 1983 to the 30 September 1985, with no clinical criteria for exclusion. The clinical and laboratory data were taken from the initial assessment of the patients in the trial, and were compared with those in the literature. The sex ratio was 10:1, only 27 were women (9%) and all were less than 70. The mean aged was 60 +/- 10 (extremes 33 to 84 years) and 80% of the population was from 40 to 70 years. Tobacco consumption was virtually constant, only 7 were non-smokers and 7% of patients smoked less than 20 packs/year; indeed consumption was very heavy with a mean of 44 +/- 23 packs/years. 14% of cases were discovered on systematic radiological examination, but 39% of these asymptomatic patients already had disseminated disease. For the 304 patients overall, despite a very variable degree of dissemination from one patient and one centre to another, 163 (54%) had disseminated disease at the outset and 141 (46%) were apparently localised. The initial metastases were often multiple: extra-thoracic nodes (21%), hepatic (23%), osseous (20%), bone marrow (23%), cerebral (9%), and others (9%); these frequencies are underestimated in view of the fact that the investigations were not over-extensive. The serum carcino embryonic antigen levels were abnormal in 32% of cases. Fibroscopy remains the main diagnostic method to provide the histological proof for 90% of patients, but 4% had thoracotomies (of whom 3% were diagnostic thoracotomies).(ABSTRACT TRUNCATED AT 250 WORDS)