Many reports indicate that prolactin has a role in puberty occurrence. The present study was developed to evaluate the action of pituitary grafts on puberty. Female rats grafted on day 21 with ‘adult’ (90 days old) or ‘young’ (21 days old) pituitaries showed precocious vaginal opening and first estrus. The puberty advancement induced by ‘adult’ transplants was due to an increase in plasma prolactin values and can be blocked by bromocriptine treatment. The puberty advancement induced by ‘young’ transplants was not associated with increased prolactin levels and cannot be blocked by bromocriptine. These results suggest the existence of two possible mechanisms in precocious puberty induced by pituitary grafts: a prolactin-dependent one and another one not directly related