The leukocytes of male patients with Fabry's disease are deficient in alpha-galactosidase. The alpha-galactosidase activity in the leukocytes of female carriers of the disease is 15 to 40 percent of the amount present in normal leukocytes. The activities of beta-galactosidase, beta-acetylgalactosaminidase, and beta-acetylglucosaminidase in the leukocytes of affected individuals are normal.