Convective cooling of human skin to 20 degrees C or less for 1 h immediately after ultraviolet-B irradiation (UV-B, 290-320 nm) results in a significant increase in erythemal threshold when erythema was observed at 4-6 h postirradiation. Cooling the skin immediately before UV-B irradiation showed no consistent influence on the erythema response. In neither case was an effect of cooling on erythemal threshold apparent when erythema was evaluated at 24 h postirradiation. These effects may be due to alterations in the diffusion kinetics of chemical mediators of inflammation, modification of vascular responsiveness, or reflect changes in temperature-dependent cellular repair or expression of UV-induced damage.