Previously, we have examined how aging affects the physiological responses of men to endurance exercise. In the present investigation, we aimed to extend our assessment of the influence of aging on exercise-induced responses by focusing on women. Ten young (20.3 +/- 0.3 years; mean +/- SE) and 10 aged (75.5 +/- 1.2 years) women performed 30 min of cycling at 60-65% of their predetermined peak oxygen uptake. Data for respiratory exchange ratio (RER), heart rate, blood pressure, rectal temperature, and plasma metabolites were collected before exercise, at the 15th and 30th min of exercise, and at 5 and 15 min postexercise. A two-way, repeated measures ANOVA with main effects of age and time was conducted on each variable. Our findings showed that age affected exercise-induced responses of each variable quantified. Although RER, heart rate, temperature, and lactate were significantly (P < 0.05) higher among young women, blood pressure and glucose values were greater among aged women. Moreover, unlike previous results noted among men where age-related differences primarily occurred during postexercise recovery, in women the effect of aging was detected during exercise itself. The data presented here indicate that aging impacts physiological responses of women to prolonged endurance exercise even when relative intensity (% of peak oxygen uptake) is held constant. Combined with our earlier study on men, these findings suggest that gender interacts with aging to determine whether age-related differences are manifested during exercise itself, or during postexercise recovery.