Human foods and animal feeds, and ingredients used for their preparation or formulation in Nigeria, were surveyed between 1988 and 1991 for the presence of the fungal metabolite and animal carcinogen aflatoxin. Groundnut and groundnut-containing materials were the most heavily contaminated, the highest value (1862 ppb) being found in a groundnut cake sample. This mycotoxin was also detected occasionally, but to a lesser extent, in some grains and cereals that are of nutritional importance in human foods and the livestock industry in Nigeria. The toxicological implications of this finding are discussed in relation to human health and animal production.