The effect of sleep deprivation on male runners (age 18.1 +/- 0.35) and volleyball players (age 17.8 +/- 0.36) has not been investigated. Therefore, we studied the possible effect of sleep deprivation in the sportsmen. The athletes performed spirometric tests at rest and then incremental exercise test on ergometer following one night sleep and one night (25-30 h) sleeplessness. Several standard measurements of spirometric function showed no significant change following sleep loss. Sleep loss raised resting oxygen uptake (VO2) in the runners and resting carbon dioxide production (VCO2) in both the runners and the volleyball players (p < 0.05). However, it left heart rate (HR), respiratory quotient (R), minute ventilation (VE) and arterial oxygen saturation (SaO2) unchanged at rest in both groups. Sleep loss decreased time to exhaustion in the volleyball players (p < 0.01). In the runners and the volleyball players, sleep loss did not alter exercise values of HR, VO2, VCO2, R and SaO2, but it reduced exercise VE (p < 0.05). We suggest that one night sleep deprivation may reduce exercise performance by decreasing exercise VE and time to exhaustion. We also indicate that sleep loss may decrease more the performance of volleyball players than that of runners.