This study was undertaken to determine the effect of high intensity exercise on the time course and magnitude of excess postexercise O2 consumption (EPOC). Six healthy male subjects performed three intermittent 2-min exercise bouts on a cycle ergometer at 108% of VO2max with 3-min rest periods (3 x 2 min). O2 uptake, blood lactate, plasma catecholamines, and rectal temperature were measured while the subjects rested in bed for 14 h postexercise, and the results were compared with those of an identical control experiment without exercise. In addition, they were studied on two separate days for 2 h after only two (2 x 2 min) or one (1 x 2 min) exercise bout. O2 uptake was significantly increased for 4 h after 3 x 2 min exercise, for 60 min after 2 x 2 min, and for 30 min after 1 x 2 min exercise. EPOC was 5.6 +/- 0.41 (1 x 2 min), 6.7 +/- 0.41 (2 x 2 min), and 16.3 +/- 3.01 (3 x 2 min), respectively. Over the first hour postexercise, EPOC was linearly related to the change in blood lactate and plasma norepinephrine. However, after exhaustive supramaximal exercise O2 consumption was significantly increased for 4 h, whereas blood lactate and plasma norepinephrine concentrations were significantly increased for only 2 h.