Introduction and objectives: The aim of the present study was to evaluate differences in plasma cortisol concentration in response to an intercalating aerobic-anaerobic exercise test in a group of physically active young people. Methods: Fourteen healthy young male volunteers performed a 40-minute exercise test at 50% of individual peak oxygen uptake on a cycle ergometer, maintaining a pedal rate of 60 r.p.m., during which they aimed to intercalate 4 explosive anaerobic phases of 30 seconds with a workload of 0.04 kg per kg of body mass at 10, 20, 30 and 40 minutes. After this first phase, and without stopping the exercise and maintaining the corresponding workload of 50% of peak oxygen uptake, the volunteers ended the exercise by pedaling at the maximum number of revolutions possible for 20 minutes. Cardiopulmonary parameters were continuously monitored and blood samples were obtained at rest, every 10 minutes during the test, and at 15 minutes during the recovery period. Results: Cardiopulmonary and metabolic responses were similar in all the participants during the test and the group tendency was to increase plasma cortisol levels significantly throughout the test (F = 5.16; p < 0.001). Plasma cortisol levels showed large interindividual differences (F = 6.74; p < 0.001). In 8 participants (57.1%), plasma cortisol levels increased during exercise and while in 6 (42.9%) minor changes with respect to resting values were observed. Conclusion: Substantial differences in plasma cortisol levels were found in a homogeneous group of young male volunteers during a successive aerobic-anaerobic exercise test, which may have implications in adaptation to exercise.