OBJECTIVE To evaluate, by examining data collected on professional basketball players during a 10-year period, the differences in aerobic capacity in function of the playing position and the impact on these parameters of the change in time regulation of 2000, which shortened the time allowed to attempt a field goal by 6 s and divided the duration of play in four quarters. METHODS Twice a year between 1994 and 2004, professional basketball players (n = 68) were studied for anthropometric characteristics and were submitted to an incremental exercise test on a cycle ergometer. Statistical analyses were carried out to determine the interaction between the playing position and the effect of the change in time regulation on the physiological characteristics of the players. RESULTS Anthropometric measurements were different in function of the playing position, the centres being taller and heavier than the forwards and the guards. Guards exhibited the highest Vo(2)max (54.0 (SE 1.6) ml/min/kg) and were the most affected by the change in time regulation of 2000 with a 19.5% increase. Significant main effects of "before" versus "after" rule changes were found for maximal and submaximal O(2) consumption, which were increased by 12.8% at ventilatory threshold, 7.3% at respiratory compensation point and 7.8% at Vo(2)max. CONCLUSIONS While anthropometric characteristics remained constant during the last decade, the change in rule of 2000 may have contributed in modifying the physiological profile of basketball players, by generally increasing their level of fitness.