Untrained healthy male volunteers were subjected to a study on the effects of exercise (bicycle ergometer, 920 kpm[kilopound meter]/min for 30 min) on GOT [glutamic oxaloacetic transaminase] [EC 2.6.1.1] isozyme (supernatant GOT [s-GOT] and mitochondrial GOT [m-GOT]) activities in plasma. Significant increases in levels of s-GOT and m-GOT activity were observed after exercise (P < 0.001). After 30 min of rest m-GOT activity almost returned to its preexercise value, but s-GOT activity did not return to its preexercise activity. Changes in the GOT isozyme activity after physical exercise are discussed.