To investigate the different ways of assessing the running velocity at which maximal oxygen uptake (VO2max) occurs, or maximal aerobic velocity (vamax), 32 well-trained runners (8 female and 24 male) were studied. The vamax and the running velocity corresponding to a blood lactate concentration of 4 mmol.l-1 (vla4) were measured during a progressive treadmill session. Within the week preceding or following the treadmill measurement the subjects completed a Université de Montreal Track-Test (UMTT). The velocity corresponding to the last stage of this test (vUMTT) was slightly higher than vamax: 6.08 m.s-1, SD 0.41, vs 6.01 m.s-1, SD 0.44 (P less than 0.03) but these two velocities were strongly correlated (r = 0.92, P less than 0.001). The heart rate values corresponding to these velocities were similar and well correlated (r = 0.79, P less than 0.01); the corresponding blood lactate values had similar mean values: 10.5 mmol.l-1, SD 2.7 vs 11.8 mmol.l-1, SD 2.5, but were not correlated. Both vamax and vUMTT correlated well with the best performance sustained over 1500 m during the season. These results suggest that the UMTT provides a value of vamax as accurately as a treadmill measurement and that either could be used to measure the running velocity corresponding to VO2max. The v1a4 was 86.6%, SD 2.6 of vamax; these two velocities correlated strongly. Thus, in well trained runners, v1a4, when measured with a well-defined procedure, corresponds to a constant fraction of vamax and depends then on VO2max and the energy cost of running.