Galactose dehydrogenase, a soluble enzyme of the mammalian liver, catalyzes the conversion of galactose to galactonic acid. This reaction, together with the subsequent formation of 3-ketogalactonic acid which can be decarboxylated to yield d-xylulose, is a newly discovered pathway for the metabolism of galactosee. This pathway may account for the oxidation of galactose observed in pathients with galactosemia.