Large populations of fungi developed in naturally infested mouldy maize stored under conditions that led to self-heating. Mould counts as high as 50 X 10⁶ propagules per gram of meal were recorded in mouldy maize meal with a moisture content of 30% stored at 10°C. The fungal population of this meal included several known toxigenic species. Pure cultures on autoclaved maize of some of these fungi isolated from the mouldy meal (Aspergillus candidus Link., A. clavatus Desm., A. fumigatus Fres., Fusarium moniliforme (Sheld.) Snyd. et Hans., F. tricinctum (Corda) Snyd. et Hans. and Trichothecium roseum Link.) were extremely toxic to chickens and rats. The natural mouldy maize meal caused significant reductions in mass gain and feed efficiency of chickens and pigs without causing mortality or significant pathological changes. Chemical analyses of the meal for aflatoxins (Aspergillus flavus Link.) and T-2 toxin (Fusarium tricinctum) were negative. In some cases chickens fed mouldy diets consumed 1,3 times more feed than the controls per gram of mass gain.