The adrenal gland of the albino rat and the Egyptian desert rodents Gerbillus pyramidum and Gerbillus gerbillus was subject to histological and histochemical studies. Compared to the albino rat, the adrenal gland of the Egyptian desert rat had a thicker capsule, its zona glomerulosa was thinner and more vacuolated, its cortex was sharply demarcated from the medulla which appeared in the form of packets of cells. Lipid droplets were larger and more numerous in the zona glomerulosa and no subglomerular zone was detected. Cholesterol and its esters were less marked in the outer cortex. Succinic dehydrogenase activity was more marked in the zona reticularis. The cholinesterase-reactive nervous network in the medulla was more complex and dense and the nerve cells were fewer. The significance of these differences is discused.