An extensive enzymatic and morphological study was performed in a 38 yr old patient with Fabry''s disease (FD). The quantitative evaluation of the enzyme .alpha.-galactosidase was important in identifying the genetic distribution of FD in the family tree of the patient under study. An enzymatic activity less than 0.5 nmol/h per 106 cells and ranging from 2.2-1.1 nmol/h per 106 cells was found in the affected males and the heterozygous females, respectively. The .alpha.-galactosidase activity in the patient''s leukocytes correlates well with the histopathological findings of the kidney and skin biopsy specimens, thus demonstrating the need for both of these special examinations for a correct diagnosis of FD.