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To provide information on the nature of the plant food diet probably available to Australopithecus africanus in the Makapansgat area, under climatic conditions similar to those at present, wild plant foods were collected during the 1980-81 dry and wet seasons. The structural toughness of the food items was estimated from force deformation during compression loading with the standard Instron Universal Testing Machine and a specially designed field apparatus. During the late wet season, in contrast with the dry season, there is relative abundance and a variety of wild plant foods available. Moreover, the most important potential plant food staples include very tough dry berries, beans and nuts, which require an average of 50-250 kg of compressive force to crack and crush them. Comparisons of food toughness measures, previously reported data on human maximum bite forces (91-158 kg), and maximum bite force values hypothesized for Australopithecus africanus (150-200+kg), suggest that although these fossil hominids would have been able to prepare orally many of the tough food species, it also appears likely that they would have had to process artifactually (with simple stone tools) the toughest of these food items to assure their survival in this environment.