The aim of this study was to evaluate the possible time-related effects of long-term monotherapy with different beta-blockers on plasma lipids in patients with essential hypertension. We studied 69 mild-moderate hypertensives, all males, aged 35-56 years belonging to the same working community. After 1-month placebo period, patients were assigned to receive propranolol 160 mg/day or atenolol 100 mg/day or bisoprolol 10 mg/day or mepindolol 10 mg/day. They were followed-up for 2 years. Blood pressure (BP), heart rate and blood samples for evaluation of total cholesterol (TC), LDL-cholesterol (LDL-C), triglycerides (TG) and HDL-cholesterol (HDL-C) were taken before and after placebo period and every 6 months from the beginning of the active treatment. All beta-blockers caused similar reduction in BP values which persisted throughout the study. None of the beta-blockers significantly affected TC and LDL-C. Propranolol caused the most pronounced changes in TG (+35-43%) and in HDL-C (-36-44%). Atenolol had the same qualitative effects but to a lesser extent (TG: +26-30%; HDL: -15-25%). Bisoprolol has more beta 1-selective than atenolol, and mepindolol, non-selective with ISA, increased TG (+15-28% and +13-23%) but did not significantly affect HDL-C. Consequently, HDL-C and TG changes appeared to be related to the ancillary properties of the different beta-blockers and, in a lesser degree, to the duration of therapy.