Blood counts of 372 Yemenite Jews of all ages were reviewed in order to clarify the epidemiology of benign leukopenia. Twenty-one percent of the total leukocyte counts were below 5.0 x 10(3) cells/mm3. Neutropenia < 2.0 x 10(3) was present in 15.4% of the blood counts, significantly lowering the average neutrophil count in the population. There was no significant variation in the prevalence of neutropenia with age. In contrast, the average lymphocyte and erythrocyte counts were normal. We conclude that leukopenia among Yemenite Jews should be defined as neutropenia rather than leukopenia, and that the phenomenon is only half as common as was previously noted. Since the prevalence of neutropenia remains constant across all age-groups, in immigrants as well as among the Israeli-born, it is unlikely to be an acquired condition.