The dose dependence of the antihypertensive effect of the beta 1 selective blocker talinolol (CAS 57460-41-0, Cordanum) was investigated in 97 essential hypertensive patients (mild to moderate) using the ambulatory blood pressure monitoring (ABPM) in a single-centre, double-blind, randomized parallel-group study. After 4 weeks of treatment a comparison was made between the once daily administered doses of 50, 100 and 200 mg as well as with placebo. The primary parameter was the mean diastolic blood pressure between 8.00 and 22.00 (dTMW). Furthermore, the duration of action of the once daily administration of 200 mg talinolol was compared with the twice daily application of 100 mg each. With regard to dTMW an increasing antihypertensive effect was determined for the dosage step from 50 mg to 100 mg talinolol/d. No further increase in the blood pressure lowering effect was observed with 200 mg talinolol/d. The highest frequency of therapy responders was found in the 100 mg group with 72.2%. Moreover it could be demonstrated, that within the dosage range of 1 x 100-200 mg Talinolol/d a significant and 24 h lasting reduction of blood pressure and pulse rate was achieved, including the early morning period. There were no differences between the blood pressure profile of the 200 mg group and the 2 x 100 mg group at the end of the 4 weeks treatment. All talinolol dosages investigated in this study were proved to be safe and well tolerated. The observed complaints classified as adverse drug reactions represented typical side effects of beta-blockers of mild to moderate intensity. It can be concluded from the results that the once daily intake of talinolol in the dosage range of 100-200 mg/d shows a reliable efficacy in the treatment of essential hypertension accompanied by a noncritical safety profile.