To evaluate the humoral and hemodynamic (both systemic and renal) effects of chronic treatment with celiprolol, six out-patients with mild to moderate uncomplicated essential hypertension received placebo for 1 month and celiprolol (400 mg qid) for 6 months. At the end of placebo and of the first and sixth month of treatment, blood pressure (BP), heart rate (HR), renal plasma flow (RPF), glomerular filtration rate (GFR), plasma renin activity (PRA), aldosterone (ALD) and noradrenaline (NA), urinary enzymes (NAG: N-acetyl-beta glucosaminidase, AAP: alanine aminopeptidase) were measured. Compared to placebo, celiprolol significantly and steadily reduced BP and HR. However, although the systemic hemodynamic effect was constant during the whole period of the study, the reduction of renovascular resistance and of plasma noradrenaline, detectable at the first month of therapy, disappeared at the sixth month. However, PRA, plasma aldosterone, GFR, and urinary enzymes did not change. These findings suggest that the antihypertensive effect of celiprolol is well maintained over the 6-month period; the drug did not exert any adverse effect on the kidney, and chronic celiprolol treatment does not influence renal hemodynamics.