Inflammation was induced in the lateral prostate of castrated Wistar rats by exposure to a sc implant of estradiol-filled Silastic tubing, followed by the addition of a dihydrotestosterone implant to restore prostatic wet weight. The presence of inflammation was correlated with increased serum PRL, elevated pituitary weight, and a greater than 2-fold increase in the lateral prostate DNA concentration. The administration of bromocriptine (4 mg/kg.day) to these animals was effective in suppressing pituitary weight and hyperprolactinemia and mitigated the lateral prostate inflammatory response. Inflammation was restored in the bromocriptine-treated hormone-implanted rats by administering exogenous ovine PRL at a dose of 2 mg/kg twice a day. The results indicate that estradiol-induced inflammation in the rat lateral prostate is mediated at least in part by the release of PRL from the pituitary.