Pacing is defined as the distribution of work during an exercise task (Abbiss & Laursen, 2008), and it is thought to be an important determinant of endurance performance. Previous studies have investigated the effects of duration/distance of the event, environmental cues, feedback and prior experience of the task on pacing during endurance exercise. Although it is well known that cardiorespiratory fitness (CF) has a strong influence on endurance performance (Bassett & Howley, 1997), its effect on pacing during endurance exercise is poorly understood. The aim of this study was to test the hypothesis that CF has a significant effect on pacing during a 30-min running time trial. (Lima-Silva et al., 2010) Thirty recreational and amateur runners were divided into three different groups (high, mid, and low CF) according to their VO2max (61.5 ± 2.1, 54.8 ± 1.8, 49.2 ± 2.1 ml min-1 Kg-1 respectively, p < 0.001) measured during a preliminary incremental treadmill test. Afterwards, these runners performed a time trial on a motorized treadmill of which they could control the speed. Subjects were instructed to run as far as possible over 30 min, and were informed of the elapsed time.. Speed, ratings of perceived exertion (RPE), and heart rate were recorded every three minutes throughout the time trial. ANOVA showed a higher performance for the High CF group (7301 ± 376 m, p<0.05) compared to Mid and Low CF groups ( 6967 ± 824, 6479 ± 667 m respectively). Two way repeated measures ANOVAs did not detect significant group x time interactions for speed (p =0.463), RPE (p =0.333), and heart rate (p =0.780). Significant main effects of time were found for speed, RPE, and heart rate (all p values < 0.001), but the only significant main effect of group was found for speed (p = 0.030) (Fig 1). Follow up tests show that all runners adopted a negative pacing strategy with a significant increase in speed at the end of the time trial. Both RPE and heart rate increased linearly during the time trial. These findings confirm that that athletes with high VO2max achieve better running performance compared to those with lower levels of CF. However, contrary to the findings of Lima-Silva et al. (Lima-Silva et al., 2010), CF does not influence the distribution of work during the time trial (pacing). The identical time course of RPE suggests that runners of different CF levels choose different average speeds in order to avoid reaching maximal RPE and, thus, exhaustion, before the end of the time trial.