Specimens derived from rat ventral prostate were cultured by an explant culture technique using differents concentrations of ovine prolactin. Sacrificed explants embedded on paraffin were sectioned for morphologic and immunocytochemical studies using antibodies against prostatic acid phosphatase, prostatic specific antigen, and wide-spectrum monoclonal keratin. Prolactin significantly stimulated the growth of these cells in the concentration range of 1 x 10(-2) ui/ml, but was inhibitory at a concentration of 1 and 0.1 ui/ml. The 1 x 10(-3) and 1 x 10(-4) ui/ml prolactin concentrations demonstrated the preservation of a glandular epithelium with a columnar shape, similar to the normal appearance of ventral prostate from rats.