The Na+, K+-ATPase test was employed to detect the capillaries in fields 17,41 and 4 of human brain. Experiments were made in subjects distributed in 4 age groups (from 22 to 86 years). The test specificity was evidenced by three groups of factors: inhibition of vascular enzymatic activity by ouabain, its preservation upon the use of an alkaline phosphatase inhibitor, equal optimal conditions for the histochemical test and biochemical studies with a "pure" enzyme. With age the intensity of the metabolism regulated with transport ATPase (in field 17 by 46.3%) was decreased. This was mainly due to the increased number of the capillaries marked by poor enzymatic activity and to a considerable reduction of the number of the vessels having fairly high activity.