1. Sensitivity of the sino-aortic baroreflex was investigated before and after acute (23 patients) and chronic (23 patients) β-adrenoreceptor antagonism in patients with essential hypertension.
2. Sensitivity was inversely related to age (r = −0·60) and systolic blood pressure (r = −0·46); a positive relationship was noted between sensitivity and initial pulse intervals (r = 0·40).
3. Sensitivity increased significantly in patients less than 40 years of age after chronic treatment. No change occurred after acute treatment or in older patients treated chronically.
4. The fall in ambulatory intra-arterial blood pressure after chronic treatment was unrelated to alteration of baroreflex sensitivity.