A comparative thermoregulatory and bioenergetic study including urine analyses of two species of southern African ground squirrels from the genus Xerus was carried out. Both X. princeps (a rock dweller) and X. inauris (a burrow dweller) are well adapted to a hot and arid environment. Both species have low resting metabolic rates (RMR) and high conductances (C). In X. princeps RMR is lower and C is higher relative to X. inauris. Both species can . increase their body temperature (T_b) in their thermoneutral zones and in ambient temperatures (Ta) above this. Salivation in both species was observed only at T_a = 38°C. At T_a = 5°C X princeps increase their oxygen consumption significantly cf. X. Inauris (p < 0,005) and regulated their T_b at 36,1 ± 0,5°C while X. Inauris maintained T_b at 34,8 ± 0,6°C. Nonshivering thermogenesis was measured as maximal VO₂ and T_b of anaesthetized squirrels injected with noradrenaline (NA). X. Inauris and X princeps responded to NA by Increasing VO₂ and T_b. Both species show a low digestible dry matter intake as predicted for desert rodents. In both squirrels percentage moisture in faeces is low but significantly (p < 0,05) lower in X. princeps than in X. Inauris. Urine analyses of hydrated squirrels showed that in X. inauris urea and Mg^{+ +} concentrations were significantly higher cf. X. princeps (p < 0,05; p<0,01). Keywords: Bioenergetics, Ground squirrels, Thermoregulation, Urine, Xerus.