By now a reasonable set of carbon and oxygen isotope data from tooth enamel has been accumulated for South African Plio-Pleistocene hominids and associated fauna. Almost all individuals measured, independent of species and importantly, environment, show significant C4 dietary inputs with some individuals showing very substantial C4 inputs. This implies interactions with grassy environments for a period of well over a million years, a period that saw environments in southern Africa shift from closed woodlands to more open, grassy landscapes. Carbon isotope analysis alone is unable to permit the important distinction between direct consumption of grasses, or indirect consumption via grass-eating animals, such as small vertebrates and invertebrates. Other chemical tools provide ambiguous results. For instance, hominid strontium/calcium distributions at Swartkrans have been interpreted as supporting omnivory, but other explanations are equally plausible. Relatively low oxygen isotope values for all hominids in comparison to associated fauna show similarities with suids, monkeys and carnivores, but the causes of these similarities are as yet poorly understood. On present evidence hominid interaction with grassland foods is secure although their exact nature remains elusive. Copyright © 2003 John Wiley & Sons, Ltd.