Controversy exists regarding the role of dopamine (DA) in the regulation of avian prolactin (PRL) secretion. Consequently, we injected apomorphine, a DA agonist, and pimozide, a DA receptor blocker, into laying and nest-deprived incubating turkeys and studied their effect on PRL secretion before (-20, -10, 0 min), during (5, 10, 20, 30 min), and after (5, 15, 30 min) electrical stimulation in the ventromedial nucleus of the hypothalamus. Apomorphine (10 mg/kg, ip) completely abolished the electrical stimulation-induced PRL increase in both laying and nest-deprived incubating hens. Pimozide (2 mg/kg, ip) potentiated electrical stimulation-induced PRL secretion in laying hens. In the two pimozide experiments, peak responses were 10.9-fold for the pimozide-treated group vs 2.9-fold for the control group, and 5.4-fold for the pimozide-treated group vs 2.6-fold for the control group. In nest-deprived incubating hens, PRL response to electrical stimulation was unaffected by pimozide treatment. These data support the concept that DA is inhibitory to the neuroendocrine system which stimulates PRL secretion in laying hens. In incubating hens, the dopaminergic inhibition is diminished, allowing for the increased PRL level observed during incubation.