Carboxylase from yeast has been purified until the final soln. has 1000 times the activity of the original extract on a dry weight basis. Carboxylase is stable at [long dash]20[degree] in aqueous 30% methanol, and treatment of such a solution with tannic acid removes protein material but not the enzyme. Subsequent adsorption on alumina separates carboxylase from saccharase, maltase, and trypsin. Yeast co-carboxylase is heat-stable but is enzymatically destroyed in unheated solns.