Several nutritional surveys have shown that African-American children have lower mean hematocrit and hemoglobin values than white children. While the high prevalence of both alpha and beta thalassemias in African-American children can partly account for the lower hematologic values, the remaining differences cannot be explained. African-American individuals have a high prevalence of traits for hemoglobin S (HbAS) and hemoglobin C (HbAC). The mean hematocrit of children with normal hemoglobin AA (HbAA) (n = 15637) was compared with that of children with traits for HbAS (n = 1197) and HbAC (n = 440). For both sexes, the mean hematocrit of subjects with HbAC and HbAS was 1.5 and 1 point lower, respectively, than that of subjects with HbAA. These differences were highly significant statistically. When the data were examined with regard to age and sex, statistically significant differences were present for all groups analyzed except the 11- through 14-year-old male group for HbAC and the 15- through 19-year-old male group for HbAS. Thus, the presence of Hb S and C traits is associated with a lower hematocrit. This reduced hematocrit may significantly contribute to the racial differences in mean hematocrit due to the high prevalence of these traits in African-American children.