ExtractHematocrit values were determined for nearly 7000 preschool children from low socio-economic backgrounds in five cities of the United States: Gainesville, Chicago, Houston, Jacksonville and Augusta. The mean hematocrit for the entire group was 36.32 %± 2.8%. Although severe anemia was unusual, the incidence of significant anemia (hematocrit <31 %) showed considerable variation from city to city, ranging from 0.6 to 7.7% and was unaffected by iron supplementation.SpeculationGeneralizations concerning the national incidence of nutritional anemia in preschool children on the basis of isolated local studies may not be warranted. Mass programs of dietary supplementation with hematinics are not indicated nationally; however, regional studies may reveal local needs.If simple, definitive and reliable laboratory techniques can be devised for use in suitably organized population groups, critical information on national health status may be obtained.Detection of a relatively large number of children with markedly elevated hematocrits is intriguing and should be investigated for relation to adult polycythemia.