ABSTRACT. This study measured Fc gamma receptor GPI, glycosyl-phosphatidylinositol (FcR) expression on polymorphonuclear leukocytes IVIG, i.v. administered IgG (PMN) and monocytes from extremely premature infants.MCF, mean log channel fluorescence Flow cytometry was used to quantitate FcRIII [cluster of PMN, polymorphonuclear leukocyte differention (CD) 161, FcRII (CD32), FcRI (CD64), CD14, WBC, white blood cell count and CD67 proteins on the PMN surface. Sixty-four pre-NICU, neonatal intensive care unit mature infants with a mean gestational age 2 SD of 26 2 2 wk (birth weight = 847 f 217 g), 12 infants born at term (gestational age = 38 + 1 wk), and 37 adults were studied.