The frequency of foods eaten by three populations of Gerbillurus tytonis and one population of G. paeba occurring in the dunes of the Namib Desert showed seasonal variation. The rodents were omnivorous, with a large proportion of their diet consisting of arthropods and plant material, but few seeds. The diets of G. paeba and G. tytonis, where they coexisted at Far East, were identical, suggesting the absence of dietary segregation. High levels of recruitment in the gerbil populations occurred during periods of high seed utilization, suggesting that seeds may be important for successful reproduction. The highest proportion of green plant material in the rodents' diet occurred during the dry part of the year, and may provide an ancillary source of water. Seeds may be too unpredictable as food source for granivory to evolve in this hyperarid desert. We suggest that because arthropods and green plant material provide more reliable food sources than seeds in the Namib Desert, G. tytonis and G. paeba have evolved an omnivorous rather than a granivorous diet, unlike the desert rodents of North America and the Middle East.