During the three years 1979-81, all patients with bronchial carcinoma of World Health Organisation types I to IV were given a questionnaire to determine occupation, smoking habits, and exposure to asbestos. Chest x rays were screened for the presence of pleural plaques. Of the men, 96.2% were current or ex-smokers, as were 71% of the women. In those who had never smoked 70% had an adenocarcinoma. In smokers the risk of getting other types was greater, but the risk of getting an adenocarcinoma was also considerably increased compared with the normal population. Of the men, 35.8% were occupationally exposed to asbestos and 15.6% were carriers of radiological plaques, a frequency five to six times greater than expected. Practically all asbestos exposed patients with lung tumours were smokers or ex-smokers and their total tobacco consumption was as high as that of non-exposed patients. The average latency from first exposure to asbestos to diagnosis of the lung tumour was 37 years. Even if strict regulations are warranted for the use of asbestos, this cannot prevent future asbestos cancers resulting from exposure that has already occurred. Elimination of smoking seems the only way to reduce such tumours.