Bromocriptine, a dopamine agonist, is now an accepted primary therapeutic agent for patients with prolactinomas and other pituitary adenomas. In this study, we demonstrated that bromocriptine inhibited the proliferation of rat somatotrophin-secreting pituitary adenoma (GH1) cells. In addition, the antitumor activity of bromocriptine was inhibited both by actinomycin D and cycloheximide, suggesting that it was dependent upon new RNA and protein synthesis. Interestingly, the results of DNA fragmentation assay and cell cycle analysis clearly demonstrated that bromocriptine induced apoptosis in GH1 cells.