This study was designed to evaluate prolactin (PRL) secretion in patients with essential hypertension. PRL secretory pattern was assessed by hourly blood sampling between 2200 and 0800 hours. Additional samples were collected at 0810 and 1000 hours (10 and 120 minutes after assumption of upright posture), as well as at 1200, 1400, and 1800 hours under normal simulated activities. No difference could be detected between the two study groups at any of the sampling times, and the number of secretory episodes were similar. Basal plasma renin activity levels were inversely related to simultaneous PRL levels in the hypertensive patients (r= -0.60, p<0.05). In the normal subjects mean overnight PRL levels were inversely related (r= -0.78, p<0.05) to the overnight urinary Na/K excretion. There was no PRL response to posture in either group. Hypertensive patients had a greater early response to the dopamine antagonist, metoclopramide than did normal subjects. Our data do not support the previously introduced concept of enhanced PRL responses to normal physiologic stimuli in essential hypertensives. However, it appears that dopaminergic control of PRL secretion may be altered in this disease state.