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The question whether evaporative water loss in snakes is affected mainly by the habitat aridity or whether it is better attributed to taxonomic position, remains controversial. To answer this question, cutaneous water loss (E-c) and skin resistance to water loss (R-s) were measured under standardized experimental conditions in four species of nocturnal vipers occupying different habitats. In the mesic-Mediterranean species Vipera, E-c increased from 0.105 to 0.175 mg cm(-2) h(-1) at air temperatures of 25 and 35 degrees C, respectively. These values were 2 to 3-fold higher than that of the desert vipers, in which E-c increased with temperature very slightly. Values of R-s in the mesic-Mediterranean Vipera (averaged 792 s cm(-1)) were two times lower than those obtained for the desert species and did not change at the different temperatures. In the desert vipers, R-s increased by different degrees with increasing air temperatures. These temperature-dependent R-s changes, which probably reflect vasomotor responses, were more pronounced in Pseudocerastes. Of the four species studied, this snake is least nocturnal and it occupies the most extreme desert habitats. These results indicate that among closely related species, E-c and R-s correlate with habitat aridity. (C) 1998 Elsevier Science Inc. All rights reserved.