The purpose of this study was to examine the effects of moderate exercise on the magnitude and duration of excess post-exercise oxygen consumption (EPOC) and catecholamine concentrations in 7 young women.The subjects performed 30 or 60 minutes of exercise (30-ME and 60-ME, respectively) on separate days at an intensity of 60% of maximal oxygen uptake on a cycle ergometer. The glucose, epinephrine and norepinephrine in the plasma, and free fatty acids and glycerol in the serum were measured at the end of the 60 min of the rest period before each exercise, immediately after the performance of each exercise and 30 min, 1, 2 and 24 h time points after each exercise.EPOC lasted for 46.1+/-25.4 and 116.1+/-79.8 min after the 30- and 60-ME, respectively. Corresponding total EPOC were 2636+/-1125 and 5208+/-1880 ml, respectively. The mean differences were statistically significant (p<0.05 each). The serum free fatty acids significantly increased immediately after the 60-ME. The serum glycerol was significantly increased immediately after the 30-ME and was also significantly increased immediately after and 30 min time point after the 60-ME. The plasma epinephrine and norepinephrine significantly increased immediately after the 30- and 60-ME, respectively. The plasma epinephrine at the 30 min time point after the 60-ME significantly correlated with the magnitude (r=0.955) and duration (r=0.897) of EPOC. Norepinephrine at the 30 min time point after the 60-ME also significantly correlated with the magnitude (r=0.774) of EPOC.The results indicate that longer duration exercise results in a greater and longer EPOC, and the plasma catecholamines may possibly contribute to EPOC in young women. Although, the overall magnitude of EPOC is small, if exercise frequency and compliance are strong, some long term benefits may accrue.