Sr NCE the genes controlling the synthesis of the ,B-chain of hemoglobins A, S, and C are allelic and inherited as autosomal codominants,' , no gender differences would be expected in the prevalence of the various genotypes. Nevertheless, a female preponderance of sickle cell trait· has been reported in two large cross-sectional surveys-one from and the other from Uganda.' In the Panama study the prevalence ofsickle cell trait was 11.35% in females and 7.2% in males. In Uganda the corresponding figures were 27.0% for females and 20.9% for males. These figures, however, represent the preva lence of sicklemia, i.e., patients in whom sickled cells appear under various in vitro testing conditions (e.g., low oxygen, sodium meta bisulfite), rather than the results of hemoglobin electrophoresis. The results thus include patients with hemoglobin AS, SS, SC, S ,B-thalassemia, and perhaps other hemoglobins, Furthermore, the screened populations were convenience samples based mostly on autopsied or hospitalized patients, including some from malaria wards. Thus the percentages reported may not be based upon a representative sample of the entire population with sickle trait. Since June, 1972, we have conducted a comprehensive umbilical cord blood screening program for neonatal diagnosis of hemoglobinopathies at our hospital.s' During the course of a prospective study of growth and