We employed an associative learning paradigm to test the hypothesis that exercise hyperpnea in man arises from learned responses forged by prior experience. 12 subjects undertook a 'conditioning' and a 'non-conditioning' session on separate days with order of performance counterbalanced among subjects. In both sessions subjects performed repeated bouts of 6min treadmill exercise each separated by 5min rest. The only difference between sessions was that the second to penultimate runs of the conditioning session were all performed with added deadspace in the breathing circuit. Cardiorespiratory responses during the first and last runs (the 'control' and 'test' runs) were compared for each session. Steady state exercise P_ETCO₂ was significantly lower (p=0.003) during test compared to control runs for both sessions (dropping by 1.8±2 and 1.4±3mmHg during conditioning and non-conditioning sessions respectively). This, and all other, test-control run differences tended to be greater during the first session performed regardless of session type. Our data provides no support for the hypothesis implicating associative learning processes in the ventilatory response to exercise in man.