A one-year open study was focused on the therapeutic effect and tolerance of spirapril in 171 patients with mild to moderate hypertension in 11 centres in the Czech and Slovak Republic. The antihypertensive effectiveness was investigated after four weeks, after 12 weeks and after 52 weeks. Only the results recorded after one year are reported. The study was completed after one year by 139 patients, incl. 120 (86.3%) with a normal diastolic pressure of 90 mmHg or less. The study was not completed by 32 patients (18.8%): because treatment was not effective--9.4%, because of undesirable effects--4.7%, 3.5% were eliminated by the investigators for various reasons (change of domicile, poor collaboration) and 1.2% because the protocol was not respected. According to the analysis "intention to treat" the diastolic pressure was normalized by monotherapy with spirapril in 25.1% of the baseline group; combination of spirapril with bopindolol led to normalization of the pressure in another 38.0% patients and in 7.0% patients normal diastolic pressure was achieved by a combination of spirapril with a hydrochlorothiazide; i.e. a total of 70.1% of the baseline group had a normal diastolic pressure after one year of treatment. In another 9.4% of the baseline group the diastolic pressure declined by 10 mmHg or more but not to normal levels. Thus normalization or effective control of pressure was achieved after one year in 79.6% patients according to the analysis "intention to treat". The combination of spirapril and bopindolol proved very effective. Patients where it was necessary to combine spirapril with bopindolol or hydrochlorothiazide had significantly higher baseline readings of blood pressure. During treatment the authors did not record in any of the groups a change of lipids, potassium, uric acid, the haemogram, liver tests or creatinine. Treatment was well tolerated and undesirable effects were rare (most frequent side effects: cough 3.5%, vertigo also 3.5%). The results of the study indicate that spirapril is an effective and well tolerated ACE inhibitor in the treatment of hypertension and its combination with bopindolol is equally suitable as the combination of spirapril with hydrochlorothiazide.