Preclinical studies have shown buspirone to have some characteristics of both a dopamine (DA) agonist and antagonist. Neuroendocrine and neurochemical studies were conducted to determine which actions occur in rats and man. Buspirone produced a dose-dependent increase in rat plasma prolactin (PRL) levels and enhanced the increase in plasma PRL levels produced by alpha-methyl-p-tyrosine and gamma-butyrolactone. Buspirone also blocked the inhibitory effect of dopamine on PRL secretion in vitro, which is consistent with the action of a DA antagonist. In a double-blind placebo-controlled study using eight normal male volunteers, buspirone (30, 60, and 90 mg) produced a dose-related increase in PRL levels 60-180 minutes later, and a significant increase in growth hormone in six of the eight volunteers, which could be evidence for a DA agonist effect in the human hypothalamus. The anxiolytic effects of buspirone could be due to either DA agonist or antagonist effects.