The clinical effect of the peripheral vasodilator prazosin (Adwersuten, GDR) was studied in 51 patients with second-stage essential hypertension. A single dose of 1 to 2.5 mg produced hypotensive effect in 48 (94.1%) patients, that lasted between 3 and 4 hours, with the lowest ABP drop occurring 1.5-2.5 hours after the administration. When prazosin was given as a course of monotherapy, its daily dose varied between 3 and 20 mg (6.7 +/- 0.6 mg). A marked hypotensive effect was obtained by the end of the first week in 91.4% of patients. A 28.6% decrease in total peripheral resistance was the principal hemodynamic effect of prazosin. No significant changes of heart rate were recorded on the group basis, while side-effects were noted in 7 (13.7%) patients (orthostatic hypotension and allergic response).