Aims: This study was designed to explore the plasma oxytocin (OT) response to exercise until exhaustion in trained male cyclists. Methods: Twelve professional cyclists (EXP group; age: 26 ± 2 years; VO2max: 4,804 ± 549 ml) and 10 sedentary young men (CONT group; age: 23 ± 2 years; VO2max: 3,146 ± 602 ml) performed a maximal incremental exercise test on a cycle ergometer. Evaluation was made of the oxygen uptake (VO2) and concentrations of blood lactate and plasma OT immediately before, during and immediately after the tests, respectively. Results: Significant increases (p < 0.01) related to exercise were recorded in VO2 and lactate concentration within each group, while no such changes were observed in OT levels. OT values, on the other hand, were significantly lower (p < 0.01) in EXP than in CONT throughout the tests. Conclusion: It was concluded that plasma OT shows no response to graded exercise until exhaustion in professional cyclists.