Tubal fluid contains high amounts of hypotaurine and taurine. These amino-acids are important for gametes and embryo survival. They are synthesized and secreted by oviduct epithelial cells in vitro. Cysteine sulfinate decarboxylase (EC 4.1.1.29) activity was identified by selective immuno-trapping using a specific antiserum in cow and goat oviduct epithelial monolayers. This result suggests that cysteine is converted to hypotaurine and taurine via cysteine sulfinic acid in these cells.