This multicenter study was designed to assess the clinical efficacy and safety of the new once-daily calcium antagonist lacidipine in the treatment of mild-to-moderate essential hypertension. Patients were randomly assigned to receive, double-blind, either lacidipine (n = 180) or hydrochlorothiazide (HCTZ, n = 182) following a 1-month placebo run-in period. Both drugs were titrated after 1 month if blood pressure was not controlled: lacidipine, from 4 to 6 mg once daily; HCTZ, from 25 to 50 mg once daily. Atenolol was added later if necessary to achieve blood pressure control. Lacidipine and HCTZ were equally effective in controlling the blood pressure levels in the majority of patients (approximately 90% after 4 months). Adverse events were those to be expected with these classes of drug and were reported in 48 (26.7%) of the patients receiving lacidipine treatment and in 34 (18.7%) of those receiving HCTZ. The diuretic produced a significantly higher incidence of hypokalemia.