Aflatoxins are common environmental hazards in all the underdeveloped countries of the tropics where they commonly contaminate food. They are toxic to most species of animals and are among the most powerful carcinogenic agents known. The liver is the principal target for toxicity. Metabolic derangements caused by aflatoxins include depression of protein and enzyme synthesis, disorder of lipid metabolism and immunological suppression. The aetiology and pathogenesis of kwashiorkor remains somewhat obscure. Similarities in the geographical and climatic prevalence of kwashiorkor and aflatoxins and similarities in the metabolic derangements caused by aflatoxins and those observed in kwashiorkor, prompted investigation of the relationship between aflatoxin and kwashiorkor in the Sudan and elsewhere in Africa. Analysis of foods from markets and in homes revealed widespread aflatoxin contamination. Aflatoxins were found more frequently and at higher concentrations in the serum of children with kwashiorkor than in those with other types of malnutrition or in normal children. Aflatoxicol, a metabolite of aflatoxin B1 was detected in serum in kwashiorkor and marasmic kwashiorkor but not in normally nourished children and only once in marasmus. Autopsy liver samples from West and Southern Africa have shown aflatoxins in all cases of kwashiorkor but not in marasmus. These findings establish relationships between aflatoxin and kwashiorkor the nature of which remains obscure but includes the possibility of a causal association.