1. In an attempt to test the hypothesis of a derangement in central catecholaminergic function in hypertensive patients, the serum growth hormone and prolactin responses to the α-adrenergic agonist clonidine (0·15 mg infused intravenously) and to l-dopa administration (500 mg orally) were evaluated in 15 hypertensive and 15 normotensive subjects matched for sex, age and body weight.

2. Whereas l-dopa elicited a growth hormone response of similar magnitude in both groups, clonidine infusion induced a significant increase in serum growth hormone in normotensive, but not in hypertensive, subjects.

3. Prolactin levels were equally suppressed by l-dopa and did not change after clonidine in either group.

4. The present study adds neuroendocrine evidence to the concept of a derangement in central α-adrenergic function in human hypertension.

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