PURPOSE: The immature neonatal immune system is thought to result in increased risk of infection. Receptors for the Fc moiety of IgG (FcgammaR) are important in antibody-mediated clearance of microbes by granulocytes and monocytes/macrophages. As an approach to understand their role in neonatal life, we compared the constitutive expression of the three Fc receptors-FcgammaRI (CD64), FcgammaRII (CD32) and FcgammaRIII (CD16)-of neonatal granulocytes with those of adult granulocytes. METHODS: Using quantitative immunofluorescence by flow cytometry, we have compared the constitutive expression of the three Fc receptors-FcgammaRI (CD64), FcgammaRII (CD32) and FcgammaRIII (CD16)-by neonatal and adult blood granulocytes. RESULTS: The proportion of FcgammaRI+ granulocytes is significanly high in cord blood compared to that of adult. However, the proportions of FcgammaRII+ or FcgammaRIII+ cells are significanly low in cord blood compared to those of adlut. CONCLUSIONS: There were differences in the expression of FcgammaR on granulocytes between cord blood and adult peripheral blood. This results suggest that the differences in FcgammaR expression may be contributed to the differences in functional activity.