The influence of experimental aluminum toxicosis on the levels of activity of adenosine deaminase and dipeptidyl peptidases II and IV in the brain and blood of rat has been studied. Two types of toxicosis were used: acute and chronic. The adenosine deaminase activity in the brain was decreased by 20-40% on 30th day of acute toxicosis, and in lower extent—at chronic toxicosis. The aluminum toxicosis influenced the activities of dipeptidyl peptidases in brain more slightly: activity of dipeptidyl peptidase II increased by 10-12% in whole brain at negligible changes in the medulla oblongata and cerebellum. In the blood plasma of animals, the adenosine deaminase activity increased by 21% both at chronic and acute toxicosis. In erythrocytes this activity decreased by 50% at acute toxicosis. At acute toxicosis the maximal increase of activity of dipeptidyl peptidase IV in the blood plasma was 35%, and of dipeptidyl peptidase II—27%.