Arterial concentrations of free fatty acids (FFA), glycerol and lactate were measured in male Wistar rats before, during and after 30 minutes exercise on a treadmill. The arterial concentration of glycerol increased 120% and lactate 340% during exercise, but fell immediately upon its termination. The arterial concentration of FFA increased only 20% during the exercise, but was followed by a sharp rise in the recovery period. Maximum FFA concentration was found after 6 minutes of recovery, reaching 70% above the preexercise level, whereafter plasma FFA fell. Using radioactivity labelled microspheres it was found that the fraction of cardiac output reaching adipose tissue after 10 min of exercise was reduced by 30-90% in relation to the resting value. After 3 min recovery, however, the fractional distribution to the same tissue was in average 300% above the value measured 3 min before termination of exercise. It is concluded that the increase in plasma FFA observed during the early recovery period is caused by increased FFA release from adipose tissue, as a consequence of increased adipose tissue perfusion in the recovery period.