Complex examination of 30 apparently healthy volunteers, 70 patients with Stages I-II hypertension and transient arterial hypertension was carried out. Impairment of blood rheologic properties and distinct decrease in the platelet activity of Na+, K+ -and Mg2+, Ca(2+)-ATPases were detected in development of hypertensive disease. In transient arterial hypertension the activity of Na+, K(+)-ATPase was increased in the erythrocyte membranes due to the fraction of old erythrocytes, while in Stage II hypertensive disease the enzymatic activity was decreased mainly in the fraction of young erythrocytes.