Monoclonal antibodies were produced against the oviductal secretory substances in 'Shiba' goats and their nature was characterized. In the ampullary region, very strong immunoreactivity with one clone (EE-1) was localized within the cytoplasm of non-ciliated cells ("secretory cells"), whereas very little or no immunoreactivity was observed in the isthmus region. This reactivity pattern was observed in both estrous and luteal phases. Immunohistochemical analysis showed the antigen to be either absent or minimally present in other organs including the alimentary canal, liver, pancreas, lung, kidney, uterus, thyroid gland, heart, spleen and spinal cord, and in oviducts of other species such as hamster, sheep and cow. The immunoglobulin isotype of EE-1 was determined as IgM with a kappa light chain. The positive reactions were eliminated by treating deparaffinized sections with periodic acid or testicular hyaluronidase. Results obtained in this study suggest that ampullary secretory cells in 'Shiba' goat oviduct contain a species- and tissue-specific antigen containing hyaluronic acid or hyaluronidase-sensitive carbohydrates.