The mammotroph or prolactin-secreting cell, due to its distinctive fine structure, large granules, and sustained survival in vitro, has been a favorite object for studying mechanisms of pituitary secretion and its control. In this review the structural basis of prolactin secretion is summarized and the proposed sequence of intracellular events involved in prolactin secretion together with their site of loaction is outlined. The available evidence validating the various steps in prolactin secretion and their regulation is summarized. Finally, some of the unresolved problems remaining for the future are pinpointed.