Activities and multiple forms of alpha-D-galactosidase of human kidney and liver in the normal and in Fabry's disease were comparatively studied using alpha-D-galactoside and alpha-D-fucoside as substrates. By isoelectric focusing alpha-D-galactosidase was shown to exist in multiple forms, one of which possesses both alpha-D-galactosidase and alpha-D-fucosidase activity. In Fabry's disease, caused by a deficiency of alpha-D-galactosidase A, we found only one form of alpha-D-galactosidase, which corresponded to form B (alpha-N-acetylgalactosaminidase) and was also able to split alpha-D-fucoside. Thus, in Fabry's disease the alpha-D-fucosidase profile was virtually unchanged, as compared with the normal. The results obtained indicate that the alpha-D-fucosidase activity is due to the action of alpha-D-galactosidase B, encoded for by an autosomal gene of chromosome 22. We suppose these data could be confirmed by revealing the significant reduction of the alpha-D-fucosidase activity in patients with alpha-N-acetylgalactosaminidase deficiency.