Effects of 20 km running on heart rate, plasma and urinary catecholamines metabolism in 4 young healthy men were investigated. Plasma and urinary catecholamine concentrations were determined by high pressure liquid chromatography. The results were as follows : 1) Immediately after the 20 km running, the concentrations of plasma free noradrenaline and adrenaline were elevated up to 1.14±0.40 and 0.12±0.07 ng/ml, respectively. These concentrations fell rapidly during the recovery period and returned to the pre-exercise values at 10 min after the cessation of running. 2) Heart rate dropped from immediately after the 20km running to 5 min of recovery period. Thereafter, however, no change was observed up to 10 min of recovery period. 3) Excretion of urinary free noradrenaline and adrenaline increased right after the 20 km running. However, it recovered pre-exercise level soon after the cessation of exercise. 4) Excretion of urinary total (free+conjugated) noradrenaline and adrenaline increastd after the 20 km running. It remained elevated for 1hr after exercise and showed slow recovery from the exercise stress. 5) Excretion of urinary conjugated noradrenaline and adrenaline showed only small increases after the 20 km running, and it increased further for 1hr of recovery period. 6) Excretion of urinary dopamine (both free and conjugated) also showed only small increases after the 20 km running, and it rose further for 1hr after the cessation of exercise. 7) Free catecholamines/total catecholamines ratio (F/T ratio) before the 20 km running was 45.7% and 54.3% (noradrenaline and adrenaline, respectively). F/T ratio resulted in an increase of 64.8% and 75.3% after the 20 km running (noradrenaline and adrenaline, respectively). However, no changes were observed in urinary dopamine.