Thirteen female cyclists/triathletes (mean peak V·O2 = 53.0 + 5.6 ml · kg-1 · min-1) using a monophasic oral contraceptive (OC) performed an endurance test (1-h cycle) at three time points of an OC cycle. Testing times were during the OC consumption phase (CONS), early in the OC withdrawal phase (WITH1) and late in the OC withdrawal phase (WITH2). Resting endogenous serum oestradiol and progesterone concentrations were measured. Power output, heart rate (HR), ventilation (V·E), oxygen consumption (V·O2), respiratory exchange ratio (RER), rating of perceived exertion (RPE), blood lactate and blood glucose were measured throughout the 1-h test. Serum oestradiol levels were greater during WITH2 compared to the CONS (p <0.05). No significant differences were present between the testing times for mean power output (172 - 173 watts), HR (163 - 166 bpm), V·O2 (41.3 - 41.7 mL · kg-1 · min-1), RER (0.93 - 0.94), RPE (14.5 - 14.8) and blood glucose concentration (5.3 - 5.5 mmol · L-1) (p > 0.05). Greater mean V·E (by 3.4 and 5.7 L · min-1) and V·E/V·O2 (by 1.0 and 2.0) values were measured during CONS compared to WITH1 and WITH2 respectively and blood lactate values (by 1.2 mmol · L-1) compared to WITH1 only (p <0.05). Despite variation in some physiological variables, there was no difference in endurance performance throughout an OC cycle in endurance trained female athletes.