Twenty-one patients with a sitting diastolic blood pressure between 100 and 114 mmHg after a single-blind 2-week placebo run-in period, started treatment under open conditions with the fixed combination of verapamil SR/trandolapril 180/1 mg o.d. for a period of 8 weeks. Patients whose conventionally measured diastolic blood pressure after 4 weeks' treatment was not normalised (diastolic blood pressure < 90 mmHg) received the higher dosage (verapamil SR/trandolapril 180/2 mg o.d.) for a further 4 weeks. Clinical evaluations including measurement of blood pressure were performed every 2 weeks. A 24-h ambulatory blood pressure monitoring (ABPM) was performed at weeks 0, 4 and 8 (end of the study). The mean office blood pressure decreased from 155 +/- 11/104 +/- 4 mmHg at baseline to 139 +/- 9/89 +/- 6 mmHg at week 8. In 12 patients (60%), the diastolic blood pressure was normalised after week 4. In eight patients, the dosage was increased and, of these, a further 25% were normalised at week 8. Response, defined as a reduction of diastolic blood pressure to < or approximately 90 mmHg (normalisation) or a decrease of at least 10 mmHg compared to baseline, was recorded in 18 patients (90%). The mean 24-h ABPM was reduced from 143 +/- 15/85 +/- 9 mmHg at baseline to 131 +/- 11/77 +/- 8 mmHg at week 8. The average systolic and diastolic blood pressure was reduced by a statistically significant amount (11/9 mmHg) during the day (8.00 am-10.00 pm) and 11/7 mmHg during the night (10.00 pm-8.00 am). Diurnal variation did not change. Only mild to moderate adverse events such as slight isolated elevations of SGPT, SGOT and potassium were observed. Two patients discontinued the study prematurely due to impotence which began during the placebo run-in period. No adverse events were serious or required any medical treatment. The fixed combination of verapamil SR and trandolapril appear to be a very effective and well-tolerated once-a-day antihypertensive medication.