Most gerbils (Gerbillinae: Cricetidae) that inhabit Mediterranean deserts are granivorous. The fat sand rat (Psammomys obesus), however, feeds almost solely on the saltbush Atriplex halimus. A parallel situation has evolved among kangaroo rats (Dipodomys; Heteromyidae) that inhabit deserts of western North America where Dipodomys microps feed almost exclusively on the saltbush Atriplex confertifolia and other Dipodomys are primarily seed eaters. Atriplex has succulent leaves but is high in electrolyte content, which can cause an osmotic burden on the animals. To overcome this problem, it has been widely accepted that P. obesus use mainly a physiological adaptation and D. microps mainly a behavioral adaptation; namely, P. obesus consume Atriplex leaves in toto and produce highly concentrated urine, whereas D. microps scrape Atriplex leaves with their teeth before consuming them and remove much of the electrolytes. However, contrary to what has been reported, it was observed that P. obesus scrape Atriplex leaves as well. The amount of leaf scrapings was related to the water content of the Atriplex. When offered Atriplex of 84% water content, they scraped off only 0.8% of the dry matter, and when they were offered Atriplex of 78% and 69% water content, they scraped off 6.4% and 14.3% of dry matter, respectively. Ash content per unit of dry matter of leaf scrapings was approximately 66% higher than that in nonscraped leaves, and Na⁺, K⁺, and Cl⁻ were 79%, 129%, and 85% higher, respectively. When P. obesus were offered Atriplex of 69% water content, scraping the leaves lowered the ash, Na⁺, K⁺ and Cl⁻ intakes by 10.9%, 13.0%, 21.4%, and 17.8%, respectively. Psammomys obesus thus have some control over the amount of their electrolyte intake and generally do not have to produce an extremely concentrated urine. This study refutes the reports that P. obesus can survive on a diet of only A. halimus mainly through their physiological adaptations.