Background: Human newborn infants display a variety of immunodeficiencies of immaturity, including diminished neutrophil adhesion, chemotaxis, and migration. Rac2, a guanosine triphosphate-binding protein, is an essential regulator of human neutrophil migration and chemotaxis. Since human subjects and mice deficient in Rac2 display deficiencies in neutrophil functions similar to newborn infants, we postulated that newborn neutrophils may be deficient in Rac2. Objectives: The aim of the study was to measure Rac1 and Rac2 concentrations in neutrophils from umbilical cord blood. Methods: Neutrophils from cord and adult blood were isolated, total cell lysates extracted, and Rac protein concentrations determined using Western blot analysis. Results: Rac2 concentrations were significantly lower in the neutrophil protein lysates isolated from cord blood compared to adult blood despite similar levels of Rac1. Conclusions: Diminished Rac2 expression in cord blood neutrophils may contribute to the defects observed in cord blood neutrophil function.