As exercise can improve the regulation of glucose and carbohydrate metabolism, it is important to establish biological factors, such as sex, that may influence these outcomes. Glucose kinetics, therefore, were compared between women and men at rest, during exercise, and postexercise. It was hypothesized that glucose flux would be significantly lower in women than men during both the exercise and postexercise periods. Subjects included normal weight, healthy, eumenorrehic women and men, matched for habitual activity level and maximal oxygen uptake per kilogram lean body mass. Testing occurred following 3 days of diet control, with no exercise the day before. Subjects were tested in the overnight-fasted condition with women studied in the midluteal phase of the menstrual cycle. Resting (120 min), exercise (85% lactate threshold, 90 min), and postexercise (180 min) measurements of glucose flux and substrate metabolism were made. During exercise, women had a significantly lower rate of glucose appearance (Ra) (P<0.001) and disappearance (Rd) (P<0.002) compared with men. Maximal values were achieved at 90 min of exercise for both glucose Ra (mean+/-SE: 22.8+/-1.12 micromol.kg body wt-1.min-1 women and 33.6+/-1.79 micromol.kg body wt-1.min-1 men) and glucose Rd (23.2+/-1.26 and 34.1+/-1.71 micromol.kg body wt-1.min-1, respectively). Exercise epinephrine concentration was significantly lower in women compared with men (P<0.02), as was the increment in glucagon from rest to exercise (P<0.04). During the postexercise period, glucose Ra and Rd were also significantly lower in women vs. men (P<0.001), with differences diminishing over time. In conclusion, circulating blood glucose flux was significantly lower during 90 min of moderate exercise, and immediately postexercise, in women compared with men. Sex differences in the glucagon increase to exercise, and/or the epinephrine levels during exercise, may play a role in determining these sex differences in exercise glucose turnover.