Aspects of the physiology of the arid-occurring otomyine rodents of southern Africa (Parotomys brantsii, Parotomys littledalei and Otomys unisulcatus) were examined, including: (1) renal function; (2) thermal physiology. Parotomys littledalei exhibited a maximum predicted urine-concentrating ability similar to other arid-occurring rodents. Maximum concentrating abilities were moderate for O. unisulcatus and low for P. brantsii. The extension of P. littledalei into the driest regions, in which it occurs allopatrically, suggests the importance of renal function in determining the distributional limits of these species. The thermophysiology of these otomyine species demonstrated a mixed ability to cope with aridity. Typical of arid-occurring diurnal rodents, all became hyperthermic at high ambient temperatures. However, none exhibited several additional thermophysiological characteristics common to arid-occurring rodents. Thus, resting metabolic rate was not lower than expected for body size, while lower critical temperatures were relatively low and the thermal neutral zone was broad. Nevertheless, the upper limit of thermoneutrality of P. littledalei was lower than that of P. brantsii or O. unisulcatus. The failure of P. littledalei to occur in hotter areas, in which P. brantsii occurs, seems to be related to its thermal physiology. Whereas renal function or thermophysiology may influence the arid extension of P. brantsii and P. littledalei, the high vulnerability of its refuges to fire damage may limit the distribution of O. unisulcatus. Reviewing the thermophysiology of the Otomyinae from more mesic habitats, we argue that their thermophysiology is more closely related to refuge type than aridity. Compared to the apparently specialized physiological mechanisms used by omnivorous or granivorous desert rodents, our study suggests behavioural adaptations such as refuge type and food selection are more important to the survival of these herbivorous desert rodents.