Amines and/or peptide-producing cells, deserving to be called paraneurons, were demonstrated in the urethro-prostatic complex of the man, rabbit, buffalo and sheep and in the uterine horns of the pig, horse and mouse, by means of histochemical, immunohistochemical, immunofluorescent and double labeling immunofluorescent techniques. In particular, the urethro-prostatic complex of the sheep contains cells producing serotonin, chromogranin A and somatostatin. Often the amine and the "marker"-protein were colocalized in the same cells. Chromogranin A- and somatostatin-containing cells were found in the uterine horns of the pig. Serotonin probably plays a role in the contraction/relaxation of the musculature of the male urogenital tract, thus regulating the urinary and spermatic flow. The function of somatostatin cells in the urogenital tract is unknown. The presence and direction of their cytoplasmic processes lead us to hypothesize a double endocrine/paracrine modality of action.