Blood pressure and serum llpoproteln concentrations were assessed In 40 men with essential hypertension at the end of a long-term, controlled intervention study (HAPPHY) after 5.2±1.4 years of treatment with hydrochlorothiazlde (n=23) or atenolol (n=17) and after a wash-out period. After withdrawal from arrtihypertenslve medication, the blood pressures of patients treated with diuretics or beta blockers rose from 142/93 and 145/91 to 159/106 and 165/104 mm Hg, respectively. At the same time, low density llpoproteln cholesterol decreased by 17 and 12 mg/dl, respectively, In the diuretic and beta blocker groups (p<0.05). In addition, total cholesterol decreased by 16 mg/dl (p<0.05) in the diuretic group, whereas high density llpoproteln cholesterol Increased by 8 mg/dl (/?<0.01) and trlglycerides decreased by 27 mg/dl (p<0.0S) In the beta blocker group at the end of the wash-out period as compared to the final phase of the HAPPHY study. The data Indicate the perslstance of llpid changes during long-term treatment with hydrochlorothlazlde and atenolol. For the first time, it was clearly demonstrated that the well-known unfavorable effects of diuretics and beta blockers on llpid metabolism are reversible after cessation of long-term therapy of several years' duration.