A brief summary is given about present-day knowledge and views on the control of prolactin secretion in mammals. This is followed by the presentation of the evidence that dopamine is the inhibitory hypothalamic transducer controlling hormone release by prolactin cells. Most of the evidence is pharmacological in nature. It is only very recently that dopamine has been found in a meaningful concentration in the blood flowing from the median eminence to the pituitary. Although the dopamine concept of an inhibitory control of prolactin secretion seems quite satisfactory, the possibility of another unrelated inhibitory control system is not excluded.