We evaluated the mortality of 835 white male and 36 female laboratory workers employed by the U.S. Department of Agriculture who died between January 1, 1970, and December 31, 1979. For males, the mortality odds ratio for all cancers was 1.0 (95% confidence interval = 0.8-1.2). Colon cancer, lymphosarcoma and reticulosarcoma, nonmalignant diseases of the blood and blood-forming organs, and suicide showed elevated mortality odds ratios. Only colon cancer showed an association with duration of employment as a laboratory worker. In an accompanying case-control study, the risk of colon cancer rose to 3.2 among those who had 20 or more years of employment as a laboratory worker. Among females, breast cancer was elevated (mortality odds ratio = 5.3; 95% confidence interval = 2.8-10.1).