A recently-discovered population of the lesser Egyptian gerbil "Gerbillus gerbillus", a rodent of extreme desert habitats inhabits an isolated area in the well-watered Nile Delta. The population has been isolated in this atypical habitat since the formation of the modern Nile Delta in the late Pleistocene-early Holocene and has since been subjected to environmental conditions that are very different from those of their typical extreme desert habitats. This study examined the renal morphology and a suite of hematological and biochemical parameters in 57 Egyptian gerbils to assess whether this isolation has resulted in any detectable structural and/or functional changes in the Nile Delta population compared with the other populations. Significant morphological changes in the kidney structure were detected among the groups, and included higher relative medullary thickness and fewer but larger cortical and juxtamedullary glomeruli with higher relative glomerular blood volume. These changes may reflect adaptive morphological and physiological changes developed following the isolation of the northern Nile Delta population that began with the encroaching mesic and estuarine conditions of the northern fringes of the Nile Delta some 12000 years before the present. Such changes appear to be related to the need to excrete excess salts associated with feeding on halophytic plant material of the northern Nile Delta habitat. The changes detected in some of the tested hematological and biochemical parameters are difficult to be explained and may be secondary to the development of the ability to get rid of excessive salt load or as an adaptation to different environments.