To investigate whether the exercise intensity affects sweating efficiency (eta sw) during exercise under mild environmental conditions, six healthy males, aged 22 +/- 2 years, performed three bicycle ergometer exercises at varying intensities (73W: Ex-1, 103W: Ex-2 and 133W: Ex-3) for 40 min under the conditions of 25 degrees C room temperature, 50% relative humidity and 0.3-0.4 m s-1 wind velocity. Heart rate, oxygen consumption, rectal temperature (Tre), mean skin temperature (Tsk; 4 skin sites) and total sweat rate were determined intermittently throughout the experiments. Moreover, heat loss by evaporation (E), radiation (R), convection (C) and eta sw were calculated using the heat balance equations. The findings concerning thermoregulatory parameters under the three experimental conditions were summarized as follows: (1) the higher the exercise intensity, the larger the values of Tre and Tsk at the end of exercise and E, R and C during exercise (2) the mean values +/- SE of eta sw were 55.4 +/- 5.1, 63.2 +/- 5.2 and 58.5 +/- 1.9% for Ex-1, Ex-2 and Ex-3, respectively. The results suggest that exercise intensity would have no effect on eta sw in this mild thermal environment.