An international trial recruited 1.049 patients from 122 investigators. After a 2− to 4-week, single-blind placebo run-in, patients were treated unblinded for 1 year. Therapy was started with trandolapril 2 mg once daily. The dose was increased to 4 mg/day if, after 1 month, blood pressure was not normalized, and then was combined with diuretics and/or calcium antagonists in increasing doses if necessary. At the cutoff point for this interim analysis. 481 patients had been treated for over 12 months and 960 for 3 months. At end point, trandolapril produced a significant decrease in blood pressure (-14 mm Hg for mean supine diastolic blood pressure). Blood pressure was normalized in 60% of the population with monotherapy. Trandolapril, alone or in combination with diuretics or calcium antagonists, was well tolerated clinically and biochemically. Only 3.9% patients reported dry cough. Withdrawals of patients from the study for treatment related reasons were 3.8%. Trandolapril had also an excellent antihypertensive effect and was well tolerated in elderly patients, in patients with glucose intolerance, and in patients with renal dysfunction.