The aim of this study was to observe the effects of exercise on plasma free fatty acids (FFA), the catecholamines (adrenaline, noradrenaline, dopamine) and leptin levels, before and after training, to determine their possible influence on the improvement of the regulation of energy homeostasis. Eleven trained rowers performed two exercise sessions (S1, S2) of 90 min each (70-75% V(.)O(2peak)), separated by a 36-week period of intense endurance training. Leptin, FFA and catecholamine plasma concentrations were measured both at the beginning and at the end of S1 and S2, and after recovery periods of 2 and 24 h. Training modified leptin levels in S2 as opposed to S1 ( P<0.001); in S1 leptin levels remained lower after a 24 h recovery whereas they returned to pre-exercise levels in S2. The respiratory exchange ratio was significantly reduced in S2 compared to S1 ( P=0.018). The FFA and leptin levels were correlated after a 24-h recovery in S1 ( r=0.87; P=0.0082), and after a 2-h recovery in S2 ( r=0.66; P=0.021). All data were expressed as the means and standard errors of the mean. In the two sessions, an immediate exercise effect was observed on the levels of the catecholamines, which did not persist after recovery. This training effect was apparent for all catecholamines in response to exercise, particularly on noradrenaline ( P=0.0006). The noradrenaline and leptin levels were correlated after a 2-h recovery in S2 ( r=-0.74; P=0.0042). We conclude that the effect of training on the response of noradrenaline to exercise seems to be involved in the delay in the normalization of leptin levels. We suggest that the amplitude of the noradrenaline response to exercise induced an increase in fat use and a rapid leptin recovery after exercise. The sensitivity of leptin to changes in the fat stores may be improved after training. Both training effects seemed to be involved in the reduction of the recovery time observed for the leptin levels.