PURPOSE To evaluate the behaviour of 24 hour blood pressure and the therapeutic efficacy of diltiazem 240mg (slow release) in mild and moderate hypertension. METHODS In an open noncomparative study 20 hypertensive patients were evaluated after two weeks of wash out and eight weeks of therapy. Diltiazem 240mg, slow-release, was used in once a day basis. The blood pressure was evaluated through casual measures and by ambulatorial (ABPM) blood pressure monitorization. RESULTS Sixteen patients (80%) reached therapeutic success (PAD nomalization or at least a reduction of 10mmHg), after six weeks of therapy. There were no changes in heart rate nor orthostatic hypotension. The mean reduction for the systolic blood pressure (PAS) was the 19.25mmHg and for PAD 11.60mmHg. The variables identified in ABPM (systolic and dyastolic load, SBP and DBP) showed significant reduction with maintenance of the circadian rhythm. CONCLUSION Diltiazem 240mg, slow release, showed significant reduction (therapeutic success = 80%) in blood pressure of mild and moderate hypertensive patients associated with excellent tolerability. The circadian rhythm has been kept. The variables measured by ABPM were significantly reduced. Diltiazem demonstrated to be an important alternative for the treatment of mild to moderate hypertension due to its beneficial therapeutic effects associated to the once daily dosage.