In vivo transepidermal water loss studies are characterized by large inter-individual variability and biased by environmental effects and eccrine sweating. An in vitro technique for measuring transepidermal water loss (TEWL) was used to compare TEWL in two racial groups--blacks and whites. In both groups a significant correlation between skin temperature and increased TEWL was found (P less than 0.01). Furthermore, black skin had a significantly higher mean TEWL than white skin, corrected log TEWL 2.79 and 2.61 micrograms/cm2/h, respectively. The difference in TEWL between the groups could because measurements were made in the absence of eccrine sweating and other vital functions. The higher TEWL in black skin could be explained on the basis of a thermoregulatory mechanism. The anatomical and physiological differences in the stratum corneum between different races are discussed.