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The sequence of species selection over the grazing period directly determines the effectiveness of different grazing systems. Knowledge of this sequence is also important in understanding the plant-animal interface. The sequence of tiller defoliation by cattle and sheep was compared for 7 range grasses at 4 different sites in South African sourveld. Defoliation frequency and height was monitored daily over a 6-day grazing period at each site. The sequence of species selection was the same for cattle and sheep although the acceptability of some grasses varied between animal species. Preferred species were always grazed first along with some (<20%) utilization of species of intermediate acceptability. When about 60% of the tillers of the preferred species had been defoliated, regrazing of these tillers commenced and the rate of utilization of intermediate species increased. Only after 80 to 100% of the tillers of preferred and intermediate species had been defoliated were tillers of the least-preferred species grazed. Sheep were more selective and tended to graze the least-preferred species later in the grazing period than did cattle. There was no difference between cattle and sheep in the frequency of tiller defoliation over the grazing period but tillers were defoliated to a lower height (P < 0.01) and more tissue removed (P<0.01) under sheep grazing. Cattle and sheep are therefore likely to differ in their potential impact upon rangeland.