The effects of diets differing in energy and water content on the energy turnover rates and water flux of four Gerbillurus species have been examined in the laboratory. Gerbillurus tytonis. a dune species, had higher than predicted daily energy expenditure (DEE) and high water turnover rates (WTR) for a small desert mammal. The large Gerbillurus setzeri, which occurs on gravel plains, has slightly lower than predicted DEE and lower WTR than the other gerbil species studied. The Gerbillurus species examined have DEE and WTR that are affected by the protein content and potential water yield of food eaten. The importance of diet selection for water and energy budgets are discussed as adaptive strategies employed for survival and reproduction within the southern African arid zone.