The levels of the branched-chain amino and oxo acids were measured in muscle and plasma after exercise and 10 min postexercise. Leucine was increased in both muscle and plasma after exercise and 10 min postexercise. The muscle levels of the branched-chain oxo acids were not increased immediately after exercise but were increased 10 min postexercise. Exercise caused a large increase in the plasma levels of the oxo acids of leucine and isoleucine that was further increased 10 min postexercise. The activity of branched-chain 2-oxo acid dehydrogenase (BCOAD) was increased immediately after exercise but returned to the control value by 10 min postexercise. The lack of correlation between the muscle and plasma levels of the branched-chain amino and oxo acids and BCOAD activity suggests that these amino and oxo acids are not the primary physiological regulators of BCOAD activity during exercise. On the other hand, an excellent correlation was found between the muscle ATP level and BCOAD activity, with the ATP content decreasing in tandem with an increase in BCOAD activity during exercise and decreasing during the recovery period after exercise.