In rats, adaptation to strenuous exercise was accompanied by phasic changes in the activities of the kallikrein-kinin system, elastase-like proteinases, and proteinase inhibitors, and total antioxidant activity in the serum, myocardium, liver, and cerebral cortex. After 30-rain physical exercises, activity of the kallikrein-kinin system decreased in the serum and increased in tissue with parallel activation of elastase-like proteinases in the myocardium and cerebral cortex. After 3-h exercises the activity of the kallikrein-kinin system showed some indications of exhaustion, especially in the myocardium and cerebral cortex. Activities of elastase-like proteinases tended to normal due to activation of txl-proteinase inhibitor and normalization of total antioxidant activity.