Aflatoxin B1 is suspected as an etiologic factor in the increased risk for primary liver cancer among workers in animal-feed processing plants in Denmark. Aflatoxin bound to serum albumin was therefore measured for feed-processing workers. Blood samples were collected immediately after vacation and after four weeks of work, and aflatoxin was quantified by competitive enzyme-linked immunosorbant assay. Seven of 45 individuals with an estimated exposure of 64 ng aflatoxin B1.d-1.kg-1 body weight were positive. Three positive workers had been unloading a cargo with an aflatoxin B1 level of 26 micrograms.kg-1 raw material. The exposure level correlated well with the job titles. Dust samples collected at different sites showed considerable variation in the amount of aflatoxin B1 (nondetectable to 8 micrograms.kg-1 dust). The exposure to aflatoxin B1 may only partially explain the increased risk of liver cancer.