The effect of acute hypobaric hypoxia on local sweating and cutaneous blood flow was studied in four men and four women (follicular phase of menstrual cycle), who exercised at 60% of their altitude-specific peak aerobic power for 35 min at barometric pressures (P(B)) of 770 Torr (sea level), 552 Torr (2,596 m), and 428 Torr (4,575 m) at an ambient temperature of 30°C. We measured esophageal temperature (T(es)), mean skin temperature (T̄(sk), 8 sites), and local sweating (ṁ(s)) from dew-point sensors attached to the skin at the chest, arm, and thigh. Skin blood flow (SkBF) of the forearm was measured once each minute by venous occlusion plethysmography. There were no gender differences in the sensitivity (slope) or the threshold of either ṁ(s)/T(es) or SkBF/T(es) at any altitude. No change in the T(es) for sweating onset occurred with altitude. The mean slopes of the ṁ(s)/T(es) relationships for the three regional sites decreased with increasing altitude, although these differences were not significant between the two lower P(B)s. The slope of SkBF/T(es) was reduced in five of the eight subjects at 428 Torr. Enhanced body cooling as a response to the higher evaporative capacity of the environment is suggested as a component of these peripheral changes occurring in hypobaric hypoxia.