Nonhormonal antineoplastic therapy can affect the endocrine system with consequent effects on the growth of hormone-sensitive tumors. Amongst anthracycline antibiotics, we have found daunorubicin and epirubicin able to acutely stimulate prolactin (PRL) secretion both in vivo, in the rat, and in vitro, from rat anterior pituitary cell cultures. Despite a similar structure, doxorubicin showed no such activity. Considering the possible role of PRL in breast cancer cell proliferation, the effects of certain anthracyclines might be viewed as an adverse drug reaction involving the anterior pituitary gland.