The purpose of this investigation was to determine the sympathoadrenal response to exercise in women after acclimatization to high altitude. Sixteen eumenorrheic women (age, 23.6 ± 1.2 years; weight, 56.2 ± 4.3 kg) were studied at sea level and after 10 days of high-altitude exposure (4,300 m) in either the follicular (n = 11) or luteal (n = 5) phase. Subjects performed two 45-minute submaximal steady-state exercise tests (50% and 65% peak O2 consumption [Vo2 peak]) at sea level on a bicycle ergometer. Exercise tests were also performed on day 10 of altitude exposure.(50% Vo2 peak at sea level). As compared with rest, plasma epinephrine levels increased 36% in response to exercise at 50% Vo2 peak at sea level, with no differences found between cycle phases. This increase was significantly greater (↑44%) during exercise at 65% Vo2 peak. At altitude, the epinephrine response was identical to that found for 65% Vo2 peak exercise at sea level (↑44%), with no differences found between phase assignments. The plasma norepinephrine response differed from that for epinephrine such that the increase with exercise at altitude (↑61%) was significantly greater compared with 65% Vo2 peak exercise at sea level (↑49%). Again, no phase differences were observed. It is concluded that the sympathoadrenal response to exercise (1) did not differ between cycle phases across any condition and (2) was similar to that found previously in men, and (3) the relative exercise intensity is the primary factor responsible for the epinephrine response to exercise, whereas altitude had an additive effect on the norepinephrine response to exercise. Copyright (C) 2000 by W.B. Saunders Company.