A new enzyme has been characterized in a cell-free extract of Bifidobacterium bifidum that catalysed the reversible phosphorolytic cleavage of beta-1,3-galacto-oligosaccharides. In the presence of Pi, the phosphorolysis reaction was favoured and was accompanied by a Walden reaction. Cleavage of the beta-glycosidic linkage gave an alpha-galactoside derivative (alpha-D-galactose 1-phosphate). The enzyme possesses a high specificity for beta-D-galactosido-(1, 3)-N-acetylglucosamine and beta-D-galactosido-(1, 3)-N-acetylgalactosamine. This purified intracellular enzyme had an estimated molecular mass of 140 kDa. The galactophosphorolytic activity on disaccharides was optimal at pH 6-6.5 and the reverse reaction was optimal at pH 5.5-6. The temperature optimum for phosphorolysis and the reverse reaction was approx. 50-55 degrees C. This enzyme is of particular interest in degrading some beta-D-Gal(1, 3) linkages and should be classified as EC 2.4.1.-.