Eight female rowers (M age = 21.0 yr., SD = 2.8), using a monophasic oral-contraceptive pill, performed a 1-hr. rowing ergometer test (intensity: 70% VO2max) during the active-pill and non active-pill phases of the oral contraceptive cycle. No significant differences were found in mean energy expenditure, oxygen consumption, respiratory exchange ratio, and heart rate during the endurance test at the two phases of the oral contraceptive cycle. Mean energy expenditure rate, carbohydrate energy expenditure, lipid energy expenditure, and blood lactate during the test were not statistically significantly different among the cycle phases. In conclusion, there was no observed difference in substrate oxidation and blood lactate level during endurance rowing at different phases of the oral contraceptive cycle in these endurance-trained rowers. Endurance-trained female athletes on oral contraceptives should not worry about the possible differences in substrate oxidation during everyday training at different phases of the oral contraceptive cycle.