In view of the clinical use of 2-bromo-alpha-ergocryptine (CB-154) during pregnancy, longterm effects of perinatal exposure to this drug on pituitary prolactin secretion and mammary tumorigenesis were studied experimentally using a high mammary tumor strain of SHN female mice. Pregnant mice were given daily subcutaneous injections of 0.3 mg CB-154 for 4 days from day 12 to day 15 of pregnancy (prenatal treatment). Another group of mice received daily dose of 0.06 mg CB-154 for the first 5 days of postnatal life (neonatal treatment). Either prenatal or neonatal treatment with CB-154 resulted in little alteration of the pattern of estrous cycle, ovarian structure and pituitary and plasma levels of prolactin. There was no difference between the control and mice treated neonatally with CB-154 in mammary tumorigenesis. On the other hand, somewhat delayed mammary tumor appearance was observed in mice treated prenatally with CB-154. These findings postulate that there is little deleterious influence of perinatal exposure to CB-154 on pituitary-ovary-mammary gland systems at advanced ages.