Apoptosis was investigated by electron and light microscopy in the anterior pituitary gland of the male Fischer rat in which hyperplasia of prolactin-secreting cells had been induced by estrogen implanted subcutaneously for 6 weeks. Counts by light microscopy of apoptotic cells and cells containing phagocytosed apoptotic bodies increased during a period of 44 h after estrogen withdrawal. Necrosis was present but was not prominent. Administration of bromocriptine after estrogen withdrawal increased apoptotic counts to nearly double those in the absence of bromocriptine. Bromocriptine caused some increase in necrosis. Apoptosis occurred in prolactin-secreting cells identified by immunostaining and in other cells. Phagocytosed apoptotic bodies were seen in folliculo-stellate and not in other cells. It is concluded that apoptosis occurs in the anterior pituitary gland and is induced by bromocriptine. Phagocytosis of apoptotic bodies is a function of the folliculo-stellate cells.