In this study we estimate the frequency of carriers of chronic (type I) Gaucher disease among Ashkenazi Jews by examining the glucocerebrosidase activity in leukocytes in a population of 635 blood donors (441 Ashkenazi) and 57 obligatory heterozygotes. Estimation using the defect in the enzyme glucocerebrosidase (beta-glucosidase) in leukocytes is complicated by the existence of considerable overlap between enzyme activity in normals and in heterozygotes. The assay was carried out with a natural substrate labeled with 14C. Discriminant analysis was used to establish an optimal cutoff point between the obligatory heterozygotes and normal (non-Ashkenazi) subjects for the purpose of estimating frequency of carriers. Applied to the Ashkenazi group, the cutoff point identified 3.17% as heterozygotes. Corrected for errors in classification, the carrier rate was estimated as 4.67%. This figure is in good agreement with a carrier rate of 4% estimated from the number of known cases of clinical Gaucher disease ascertained in Israel.