A multicenter study was performed in 919 hypertensive patients, 780 of whom could be evaluated. Patients in group I (n = 482) were treated with Aldactazine alone (altizide + spironolactone, 2 tablets per day). The other 298 patients (group II) were treated with 1 or 2 tablets per day of Aldactazine plus a conventional antihypertensive agent, e.g., a beta blocker, alpha-methyldopa or clonidine. After 45 days of treatment with Aldactazine alone, mean systolic and diastolic blood pressure (BP) decreased by 15 and 14%, respectively, vs baseline values. The addition of the other antihypertensive agent decreased BP further; however, the best results were obtained with the combination of Aldactazine and clonidine. With this combination, systolic and diastolic BP decreased by 16.6 and 18%, respectively, vs baseline. In terms of adverse effects, a few cases of gastrointestinal disturbances and orthostatic hypotension were reported.