A case-control study of nasopharyngeal carcinoma was conducted in northeast Thailand, a region which shows an intermediate risk for this neoplasm. The study was conducted to investigate the importance of environmental exposures, particularly salted fish consumption, cigarette smoking, alcohol drinking, and occupational exposure to smoke or dust, as risk factors for the disease. Data from 120 nasopharyngeal cancer cases and the same number of hospital-matched controls indicated that consumption of sea-salted fish at least once a week was a significant risk factor (odds ratio, 2.5; 95% confidence interval, 1.2-5.2). Agricultural workers were also at significantly higher risk (odds ratio, 2.8; 95% confidence interval, 1.3-6.2), and working in agriculture or as a woodcutter was associated with an even higher risk (odds ratio, 8.0; 95% confidence interval, 2.3-28.2). There was no association between nasopharyngeal carcinoma and alcohol drinking or cigarette smoking.