The reaction of cyclic nucleotides in blood to an orthostatic position, furosemid administration, and submaximal bicycle ergometry load was studied in 20 healthy individuals and in 50 patients with hypertensive disease. A special group was composed of 25 patients the disease in whom was marked by crises. It is shown that a walk of one hour and intravenous infusion of 40 mg of furosemid caused an increase in the blood cAMP but did not change the level of cGMP. During a bicycle ergometry load the levels of cGMP and cGMP increased to an equal measure and returned to their initial values 30 min after its cessation. In patients with arterial hypertension the cGMP system becomes most functionally mobile, whereas the cAMP level, if it increases, does so at a later term after the effect of the stimulus begins. The increased cGMP level is maintained for quite a lengthy period of time after the load is discontinued. In patients suffering from hypertensive disease with crises the cAMP/cGMP ratio, which is reduced at rest also, diminishes still more in an orthostatic position and particularly during a crisis. The role of changes in the metabolism of cyclic nucleotides and their sensitivity to regulatory factors in the pathogenesis of arterial hypertension is discussed.