Primary antibody deficiency (common variable immunodeficiency, Hyper IgM, X-linked agammaglobulinemia and selective Ig A deficiency) is a group of heterogeneous diseases characterized by defective antibody production. In primary hypogammaglobulinemias, particularly in patients with common variable immunodeficiency there is an increased generation of reactive oxygen species from monocytes which may be important for both immunopathogenesis and clinical manifestations. The generation of toxic oxygen metabolites may contribute to inflammation and tissue damage associated with phagocytic infiltration, and play role in the pathogenesis of malignancies, autoimmune disorders, acute and chronic pulmonary diseases seen in these patients. In primary immunodeficiencies and functional antibody deficiencies, IVIG act as replacement therapy and several mechanisms of IVIG action have been postulated. In vitro studies with human granulocytes showed stimulation of respiratory burst and promotion of bacterial killing by IVIG. In adult patients with primary humoral immunodeficiency, treated with IVIG showed that IVIG does not affect superoxide generation. We investigated superoxide generation from PMNL in 35 children with hyper IgM syndrome, XLA, CVID and IgA deficiency and 13 healthy children. We also explored the effect of IVIG administration on superoxide generation from granulocytes, white cell count, absolute neutrophil count, absolute lymphocyte count and quantitative CRP levels. There was a substantial increase in superoxide generation from PMNL in patients with XLA, CVID and IgA deficiency. Comparison of the superoxide generation before, 24 hours and one week after IVIG treatment showed no difference. In patients with CVID, quantitative CRP levels before and 24 hours after IVIG revealed significant difference. Other parameters were not changed. It can be concluded that enhanced superoxide generation in patients with XLA, CVID, Ig A deficiency may result from silent activation of the phagocytic system which does not give clinical symptoms; and administration of IVIG in vivo (within the serum concentrations) has no impact on superoxide generation of granulocytes in patients with primary antibody deficiencies.