As part of a comprehensive risk assessment study for fumonisins, reliable data on exposure of populations to these dietary toxins must be obtained. To assess the extent of worldwide exposure, the published literature on the contamination of food and feed supplies has been reviewed and supplemented with unpublished material from various international sources. Fumonisin contamination of corn and corn-based products occurs in many countries. Animal mycotoxicoses such as equine leukoencephalomalacia and porcine pulmonary edema are caused by heavily contaminated animal feeds. For example, as much as 330 micrograms/g fumonisin B1 (FB1) has been found in swine feed. Although commercially available refined corn products for human consumption are generally contaminated at levels below 1 microgram/g FB1, individual products in certain countries can reach far higher levels. Health risks associated with consumption of these products depend on the extent to which they are consumed in a varied diet. Home-grown corn in certain rural areas, where it also constitutes the staple diet, can be contaminated at > 100 micrograms/g. Consumption of corn contaminated at these high levels has been associated with a high incidence of esophageal cancer in these areas.