Approximately ten years ago, it was shown that when hypertension was induced in dogs by a Goldblatt clamp, the carotid sinus was reset, becoming insensitive to the elevated pressure. Is it then conceivable that antihypertensive therapy may result in a lowering of this "barostat" setting, permitting discontinuation of therapy? The US Public Health Service Cooperative Study of Hypertension provided an opportunity to evaluate this question. Sixty-nine "responders" to various antihypertensive agents had their medications discontinued after an average response period of more than two years, with uninterrupted recordings of the pressure at home. Twenty-five patients remained responders (average diastolic pressure below 90 mm Hg) for at least five months. Of this group, nine required reinstitution of therapy, 5 to 24 months later, due to the gradual rise of their diastolic pressures.