A quantitative analysis of occlusal microwear on the protoconal facets of maxillary permanent second molars of southern African specimens of <i>Australopithecus</i> and <i>Paranthropus</i> reveals that the latter display significantly greater numbers of microwear features as well as significantly higher percentage incidences of pitting on both Phase I and Phase II facets. Wear scratches also tend to display significantly greater degrees of directional heterogeneity on <i>Paranthropus</i> crowns; this increased variability of jaw movement through both Phase I and especially Phase II of mastication may reflect differences in the mechanical properties of the food items triturated by these two taxa. Wear scratches are, on average, signficantly shorter but wider, and pits are significantly larger on the occlusal surfaces of <i>Paranthropus</i> molars. Comparisons with microwear feature dimensions recorded for extant primates suggest that the diet of <i>Paranthropus</i> entailed the mastication of harder items than composed the dietary staples of <i>Australopithecus</i>. Taken in conjunction with the differences in dental proportions and craniofacial morphology exhibited by <i>Australopithecus</i> and * 2Paranthropus*1, the details of occlusal microwear indicate that the diets of these taxa were qualitatively different. The inferred dietary differences and the differences in trophic adaptations do not appear to be related solely to purported differences in estimated body sizes. -- AATA