Vasoactive intestinal polypeptide (VIP) binding sites were localised in sections of guinea pig genital tissues using [125I]VIP and quantitative in vitro receptor autoradiography. A moderate density of binding was demonstrated in the epithelium of the prostate gland, seminal vesicles and in the testes. Moderate to high VIP binding also occurred in the epithelial lining of the oviduct, uterine glands, cervix and vagina. The binding sites appear to have a dissociation constant (Kd) of 0.36 nM and maximum receptor density (Bmax) of 60.5 x 10(-3) fmol/mm2 in sections of the uterine horn. The results indicate that VIP may have a role in the secretory functions of the guinea pig genital tract.