A number of species of fungi were isolated from millet (Pennisetum typhoides Staph and Hubb) and grain sorghum (Sorghum vulgare Pers) obtained from the households of patients suffering from onyalai. Several proved to be toxic to rats and chickens, including Phoma sorghina (Sacc.) which was the predominating fungus. Cultures of P. sorghina grown on maize and wheat were added to standard rations at concentrations of 5-30%. When fed to day-old New Hampshire chickens, the majority died within 4 days, exhibiting traces of blood on the beak and the cloaca. Rats given 10% or more of the mouldered material in the diet developed thrombocytopenia after 14 days which was followed by haematuria, epistaxis, melaena, and death. Pathological, including histological examination, revealed extensive damage to the fascular system which resulted in widespread haemorrhages.