PURPOSE--Evaluation of the efficacy and tolerability of nifedipine oros in patients with mild to moderate essential hypertension without major target organ damage and the anti-hypertensive effect along the 24 hours. METHODS--Two hundred and three patients were studied. After two weeks placebo running period single dose of nifedipine oros (30 mg/day) was administered for 8 weeks. At the end of the 4th week, the non-responders (diastolic blood pressure > 90 mmHg or reduction in diastolic pressure < 10 mmHg), had the dosage increased to 60 mg/day. Laboratory tests and 24h blood pressure monitoring (60 patients) were performed at the beginning and at the end of the study. RESULTS--One hundred and ninety one patients completed the study. Fifty nine percent were considered responders at the end of the 4th week with nifedipine oros 30 mg/day and 41 needed dosage increment to 60 mg/day. At the end of the 8th week, all patients were considered responders to nifedipine oros. The blood pressure control extended throughout the 24h of the day. The most common adverse events were edema (14.6) and headache (12.4). Good and very good tolerability were informed by 85 of the patients. CONCLUSION--Nifedipine oros was able to control blood pressure efficaciously along the 24h period without important side effects. The possibility of once day dosage, increases the patient adherence to anti-hypertensive therapy.