The measurement of transepidermal water loss (TEWL) is an important noninvasive method in order to assess the barrier function of the stratum corneum. As a consequence, TEWL has been found to be a very useful technique for studying skin irritation induced by various physical and chemical effects. Exposure of the skin to chemicals (detergents) and physical conditions (occlusion and stripping) generally results in an increase of TEWL. Until recently the only commercially available TEWL instrument was the Evaporimeter® developed by ServoMed (Sweden). The instrument is based on the open chamber system with two humidity and temperature sensors which measure the water evaporation gradient at the surface of the skin. Recently a new commercially available instrument based on the same physical principle of measurement was developed by Courage and Khazaka (Tewameter®, FRG). Our aim in this study has been to compare the measuring capacities of both instruments. The accuracy, sensitivity, variability and reproducibility of both instruments were compared in vivo under identical conditions on normal skin and skin damaged by external conditions. The influence of external and environmental factors such as air and probe temperature, relative humidity, air turbulence and pressure of application was evaluated for both instruments. Finally, the two instruments were compared in practice when following the increase in TEWL of the skin after stripping, occlusion and exposure to irritant household detergents. A very good correlation (r = +0.97) was found between the results of the two instruments over a wide range of TEWL value