1. In order to evaluate whether treatment with different antihypertensive drugs would affect plasma fibrinogen levels, 118 mild to moderate essential hypertensive subjects, all males, aged 18 to 65 years, were randomly treated with amlodipine 10 mg, atenolol 100 mg, hydrochlorothiazide 25 mg or lisinopril 20 mg, all given once daily for 8 weeks. 2. Before and after 8 weeks' treatment, blood pressure (BP), heart rate (HR), fibrinogen, total cholesterol (TC), HDL-C, LDL-C, triglycerides (TG), plasma glucose, plasma uric acid, serum creatinine and serum potassium were evaluated. 3. All four medications significantly reduced BP values, although the BP lowering effect of lisinopril, amlodipine and atenolol was significantly greater compared with that of hydrochlorothiazide. 4. Plasma fibrinogen levels were unaffected by atenolol, hydrochlorothiazide and amlodipine, whereas they were significantly decreased by lisinopril (-11.2%, P = 0.002). This fibrinogen lowering effect was more evident in smokers (-17.7%) than in non smokers (-7.4%). 5. Atenolol and amlodipine did not significantly affect plasma lipids, hydrochlorothiazide increased TC, LDL-C and TG and reduced HDL-C; lisinopril increased HDL-C and decreased TC and LDL-C. 6. Hydrochlorothiazide increased plasma glucose and uric acid concentrations, which were unaffected by the other drugs. The diuretic also reduced serum potassium. 7. The results of this study indicate that lisinopril reduces levels of plasma fibrinogen and confirm that different antihypertensive drugs may elicit different metabolic effects, which may variously influence the overall risk profile of the hypertensive patients.