The detection of immunoreactivity to bombesin-like peptides in endocrine-paracrine cells from normal and pathological prostates suggest they have a regulatory role over this structure. With the purpose of explaining the action of these peptides on the prostate tissue an analysis is made of the bombesin effect on single-layer cultures of normal (rat ventral prostate) and tumoral (PC-3 cell line) prostate tissue. After performing morphological studies through phase contrast microscopy, as well as using cell counts and immunohistochemical techniques (Ki-67) to study the influence of bombesin on cell proliferation, this has been shown to stimulate prostate cells proliferation "in vitro". This response was revealed with greater intensity at bombesin concentrations of 0.5 nM/ml on the rat ventral prostate and bombesin 1 nM/ml on the PC-3 cell line. No morphological differences were observed between the controls and the bombesin-containing microwells in the rat ventral prostate, but some greater size cell elements with irregular shape were seen in the PC-3 cultures, as well as an increased number of mitotic division shapes in the wells filled up with bombesin.