Comparative water-turnover rates of Gerbillurus tytonis, G. p. paeba and G. setzeri were determined in the field at different seasons and localities. All species are omnivorous, selecting food opportunistically. During March there was no significant difference in water flux among species, although water flux decreased with body size. Water flux of G. tytonis decreased from 178 0 ml/kg/day in November to 98·4 ml/day/kg in March. Coastal populations of G. p. paeba showed a markedly higher water-turnover rate compared to inland populations.