This case-control-study, carried out in two University clinics, comprised 200 men (mean age 57.5 +/- 10.8 [range 33-89] years) with squamous epithelioma of the larynx (44.5%), oral cavity (23.5%), oropharynx (24%) or hypopharynx (8%) and 800 controls. Enquiries were directed at social status, life style and occupational exposure to substances such as asbestos, solvents, wood dust and cement. The peak incidence of these cancers was from 50 to 60 years of age. The proportion of unmarried or divorced men among the cancer patients was more than twice as high as in the controls (25.8% vs 11.8%; P less than 0.001). The proportion of cancer patients who had completed technical college or university education was significantly lower than in the controls (9.6% vs 24.4%; P less than 0.001). Tobacco and alcohol consumption by the cancer patients was roughly twice as great as in the controls: the cancer patients admitted to an average cigarette consumption of 43.2 +/- 27.9 pack years as compared with 20.1 +/- 26.7 pack years for the controls (P less than 0.001), and an alcohol intake of 69.2 +/- 58.1 g/d as compared with 29.8 +/- 27.5 g/d for the controls (P less than 0.001). Both these factors--drinking alcohol and smoking cigarettes--acted independently of one another to raise the relative risk of squamous epithelioma of the upper respiratory or digestive tract. The effects of alcohol and tobacco on cancer risk were multiplicative rather than merely additive. Enquiries into diet failed to reveal any clear differences tending to incriminate any particular food. Long-term exposure to cement dust was linked with an increased risk of cancer.