Dockers who unload aflatoxin contaminated products in Esbjerg harbour (Denmark) are potentially exposed to aflatoxins in the inspired dust. In order to assess the extent of exposure for aflatoxin B₁ in these dockers, samples of urine were collected before and after unloading. These samples were analysed by radioimmune analysis by means of a monoclonal antibody to aflatoxin B₁. Two groups of dock workers participated in the present investigation. One group unloaded a contaminated cargo while the other unloaded a corresponding cargo which was not contaminated. The dock workers had not been employed unloading contaminated cargoes for more than two months prior to the investigation. Excretion of antigenic material occurred in both groups. This corresponded to 0.2-2.3 ng aflatoxin B₁ per mg creatinine. The excretion was, on the whole, not occupationally determined but it was impossible to exclude additional occupational exposure. A group of laboratory assistants who were not occupationally exposed excreted corresponding quantities of the antigen. The literature which describes excretion of aflatoxins in man is discussed on the basis of the results of this investigation.