In a double-blind, placebo-controlled cross-over study, the plasma atrial natriuretic peptide (ANP) levels of nine young and ten elderly hypertensive patients were compared after placebo and after treatment with 120 mg verapamil given three times daily over 4 weeks. During placebo, plasma ANP levels proved to be higher in elderly patients than in young subjects. Chronic treatment with verapamil induced a rise in ANP levels in both young and elderly patients with hypertension.