Quantitative analysis of microwear features preserved on the occlusal surfaces of the M2s of southern African specimens of Australopithecus and Paranthropus (the so-called 'gracile' and 'robust' australopithecines) reveals that there is no striking relationship in either taxon between occlusal facet inclination and the incidence of wear features. Within each taxon, Phase I and Phase II facets tend to differ in a similar manner in the total number of wear features, the percentage frequency of pitting, and in the orientation of wear scratches. Nevertheless, Paranthropus molars tend to display significantly greater numbers of microwear features on both Phase I and II facets than do Australopithecus homologues, and Paranthropus molars also evince significantly higher proportions of occlusal pitting on these surfaces. Paranthropus and Australopithecus crowns also differ significantly in the degree by which the occlusal wear scratches vary in their orientation. On each facet, Australopithecus tooth scratches display a greater degree of directional similarity. The differences between the Phase I and Phase II facets of Australopithecus and Paranthropus M2s suggest that the dietary items involved in the production of these observed patterns differed also. The diets of these Plio-Pleistocene hominids appear to have been qualitatively dissimilar.