The after-effects of night work on physical performance capacity and sleep quality were studied. Ten younger (age < or = 34 years) and eight older (age > 34 years) experienced shift workers were examined. Subjects performed cycle ergometer tests at an exercise intensity requiring 70% of the individual maximal oxygen uptake. Two conditions were studied: a baseline condition, i.e. the last day of a 4 days-off period, and a recovery condition after a period of seven consecutive night shifts, i.e. the second day-off after the night-shift period (32 h after leaving the night-shift period). Sleep quality of the sleep period preceding the test was also measured for both conditions. During the recovery condition the endurance time (i.e. time to exhaustion) was reduced by an average of 20% (-160s, P < 0.05) for the older shift workers only. In both age groups exercise ventilation, heart rate, oxygen uptake, perceived exertion and sleep quality remained unaffected. These findings support the hypothesis that the aging shift worker is faced with increasing complaints, even after the night-shift period. However, to clarify the mechanisms responsible for these after-effects of night work, further extensive studies must be designed.