The authors describe two cases of clinical Fabry's disease. The first patient presents a deficiency of alpha galactosidase and a urinary excretion of ceramide trihexosides and dihexosides ; the second patient had a normal alpha galactosidase and normal excretion of urinary lipids. In this latter case the Km and the activity of the enzyme measured at different pH were similar to those of normal enzyme. The other lysosomal enzymes, beta galactosidase, beta glucosidase, hexosaminidases A and B, alpha fucosidase, arylsulfatases, phosphatase acids were also measured in patient 2 and all have normal activities. There is no urinary excretion of glycolipids or mucopolysaccharides. Yet this patient has an accumulation of material in his fibroblasts and renal cells. The authors also present a genetic study.