A thermally regulated Plexiglas chamber was designed for investigation of transcutaneous diffusion of N2 and helium (He) in the human hand. Influence of cutaneous blood flow in this process was studied simultaneously with gas diffusion measurements. Changes in cutaneous blood flow (Q, in ml X min-1 X 100 ml tissue-1) were effected by altering ambient temperature (T) from 20 to 40 degrees C (Q = 0.08 X 100.07T). We found that the rate of inert gas diffusion through human skin, expressed as conductance (G, in ml STPD X h-1 X m-2 X atm-1), increases exponentially as a function of blood flow, and was indistinguishable between He and N2 (G = 21.19 X 100.0124Q). The permeability, diffusion coefficient per unit diffusion distance (D/h, in cm/h), also rose exponentially as a function of blood flow. But permeability for He (D/h = 0.1748 X 100.0203Q) was greater than that for N2 (D/h = 0.1678 X 100.0114Q). As cutaneous blood flow rises, because of increased temperature, the apparent diffusion distance falls linearly for both N2 and He. The change is more prominent for He than for N2 diffusion. Estimated replacement time for the body stores of N2 by transcutaneous diffusion alone was shortened from 26.8 h at 31 degrees C to 15.1 h at 37 degrees C. It is suggested from this study that beneficial results may be derived during decompression procedure 1) by maintaining an appropriate transcutaneous pressure gradient of inert gases, and 2) by elevating ambient temperature.