SUMMARYIn order to investigate dopaminergic activity in two types of human obesity, childhood‐ and adult‐onset, we have studied the responses of plasma TSH and prolactin to domperidone, a dopamine receptor antagonist, in 12 patients obese since early childhood, 12 patients with adult‐onset obesity, and in 12 lean controls. All subjects were females. In childhood‐onset obese patients the responses of plasma prolactin and TSH to antidopaminergic stimulation were lower than those of adult‐onset obese patients and lean controls. Conversely, the stimulus elicited a normal response of plasma prolactin and an exaggerated response of plasma TSH in adult‐onset obese patients. These data indicate the presence of differing dopaminergic tone in the two types of hu