Summary:Strains ofAspergillus flavusrecently isolated from coconut products were cultured on grated coconut. The aflatoxin content of serial cultures was found to vary significantly with duration of incubation and for some strains to show more than one phase of increase of aflatoxin content. The occurrence of these variations indicates that the study of aflatoxigenic capacity of strains or of the capacity of a medium to support toxin production, should be based upon a knowledge of the pattern of variation of toxin content with duration of incubation of the cultures under the experimental conditions used. Assay of toxin level in a culture after one period of incubation could lead to erroneous conclusions about the identity or quantities of toxin components which the strain is able to produce.