The influence of hypertension, and its treatment, on circulating lipid and fibrinogen (Fib) concentrations in patients with essential hypertension was investigated. The lipid profile and Fib levels were measured in 353 patients (131 men) with essential hypertension. Their median age was 60 years (range: 18-85 years). All patients had normal results from liver, renal, and thyroid function tests. There were 162 patients (45.9%) who were not receiving antihypertensive treatment. Of the remaining patients, 117 were taking 'lipid-hostile' beta-blockers, thiazide diuretics) antihypertensives and 74 were taking 'lipid-neutral' (angiotensin-converting enzyme inhibitors, calcium channel blockers, angiotensin-II receptor blockers) agents. Patients who were taking 'lipid-hostile' antihypertensive drugs had significantly higher plasma Fib concentrations when compared with those taking 'lipid-neutral' antihypertensives or those not receiving antihypertensive treatment. These differences were not attributable to established factors that influence plasma Fib levels, since when smokers and patients with diabetes mellitus and/or vascular disease were excluded, the difference remained significant. In addition, in these more homogeneous groups, patients receiving 'lipid-neutral' treatment had significantly higher serum high-density lipoprotein (HDL) cholesterol levels when compared with both those taking 'lipid-hostile' antihypertensives and untreated ones. There were no significant differences in the other lipid variables, independently of the presence/absence or the type of antihypertensives. These results suggest that antihypertensive drugs have additional effects, beyond lowering blood pressure, on other vascular risk factors, like Fib and HDL. These effects may depend on the type of drug used.