Previous studies have shown that controlling the diastolic blood pressure (BP) for 6 months frequently permits the use of fewer drugs in lower doses in most patients with moderately severe and severe systemic hypertension. Prompted by these observations, the dosage of chlorthalidone (monotherapy) was decreased in a stepwise fashion and then discontinued after the diastolic BP had been maintained below 85 mm Hg for 6 months in 67 patients with mild systemic hypertension (diastolic BP 92 to 104 mm Hg). These patients have been followed for 48 months. Initially, a dose of 25 mg/day of chlorthalidone was just as effective as 50 mg in controlling the diastolic BP in all patients, and it was not until the dose was reduced to 12.5 mg/day that the diastolic BP increased in 8 patients. Annoying symptoms and metabolic side effects were decreased or eliminated. Chlorthalidone therapy was discontinued in 36 of the 67 patients. The ability to discontinue therapy in these patients suggests the possibility of intermittent, rather than continuous, lifelong therapy.