The purpose of this study was to examine the effect of ambient heat on the decrease in blood lactate concentration ([LA]bl) during passive and during active recovery. Ten trained men performed six 1-min bouts of exercise at 100% VO2peak on a cycle ergometer, with 1-min rest between the bouts. Each subject exercised twice in thermoneutral (22 degrees C, 40% RH, TN), and twice in hot (35 degrees C, 30% RH, H) conditions. Exercise was followed by either 40 min of passive recovery (sitting) or by 20 min active recovery (cycling at 35% VO2peak) and 20 min passive recovery, named thereafter, 'active recovery'. Capillary blood lactate was measured before, 1 min after, and every 5 min during recovery. Heart rate (HR), rectal and skin temperatures (Tre, Tsk) were monitored continuously. VO2 was measured prior to exercise, during the last exercise bout, the first 10 min of recovery, and periodically thereafter. Post-exercise [LA]bl was similar in all treatments (13.5 +/- 1.8, 13.0 +/- 1.3, 14.8 +/- 4.1, 13.3 +/- 2.6 mmol.l-1 for TN-active, TN-passive, H-active and H-passive, respectively). [LA]bl was significantly lower during active, compared to passive recovery in both, TN and H conditions. Environmental heart did not independently affect [LA]bl during passive or active recovery. Exercise resulted in an elevation in Tre in all treatments, with a significantly higher Tre during active recovery in H compared to the other sessions. Likewise, no differences in HR and in VO2 were observed between H and TN conditions during active nor during passive recovery.(ABSTRACT TRUNCATED AT 250 WORDS)