Potential risk factors for hepatocellular carcinoma were investigated in a case-control study among inhabitants of north east Thailand. Sixty-five cases from 3 hospitals, with matched controls, were included. Infection with hepatitis-B virus was the major risk factor-chronic carriers of HB surface antigen had an estimated relative risk of 15.2. Infection with hepatitis-C virus appeared to be rare. No increase in risk was found with recent aflatoxin intake, as estimated by consumption of possibly contaminated foods, or by measuring aflatoxin-albumin adducts in serum. Regular use of alcohol (2 or more glasses of spirits per week) was associated with a non-significant elevation in risk (o.r. = 3.4, 95% c.i. 0.8-14.6), but the number of regular drinkers in the population was small. The meaning of an apparent protection conferred by certain food items is uncertain, but a possible role of betel nut in the aetiology deserves further investigation.