A study of cancer risk among male employees at 241 livestock feed processing companies in Denmark was conducted on the basis of a data linkage system for detailed investigation of occupational cancer providing employment histories back until 1964, established at the Danish Cancer Registry. Crops imported for feed production have often been contaminated with highly variable concentrations of aflatoxins; an estimated average concentration of at least 140, g aflatoxin B1 kg-1 prepared mixed cattle feed prevailed in the past, yielding a daily intake for workers via the respiratory route of - 170 ng. Risk was established on the basis of cancer cases among male workers, whose employment in one of the companies was the job they had held for the longest time since 1964. Elevated risks for liver cancer and for cancers of the biliary tract were observed, which increased by two- to three-fold significance after a 10-year latency. Exposure to aflatoxins in the imported crops was judged to be the most probable explanation for these findings, although the influence of lifestyle factors, e.g. alcohol consumption on the results cannot be fully disregarded. Increased risks for salivary gland tumours and multiple myeloma were also detected. However, due to multiple comparisons carried out in this study these new associations must await further confirmation. A decreased risk for lung cancer was observed; despite possible negative confounding due to the smoking habits of the employees, the lung does not seem to be a target organ for the carcinogenic effect of inhaled aflatoxins in humans.