Agammaglobulinemia is characterized by failure of B-cell differentiation (hypogammaglobulinemia) and increased susceptibility to bacterial infections. The present study was set up in order to evaluate the effectiveness of intravenous immunoglobulin (IVIG) treatment on the incidence of pneumonia in patients with agammaglobulinemia. We carried out chart reviews of 23 patients with agammaglobulinemia (mean age 11.5+/-5.4 years), who had been observed in a 22-year period (July 1981-January 2003) in Iran's referral center for primary immunodeficiency disorders. Nineteen of these 23 (82.5%) had been infected with pneumonia at least once before receiving the immunoglobulin treatment and 11 of them had experienced multiple episodes. During treatment with gamma-globulin - over a mean period of 6.8+/-4.1 years (range: 0.8-15.3 years) - the incidence of pneumonia requiring treatment or hospitalization decreased from 0.82 to 0.12 per patient per year (P=0.006). During IVIG replacement, hospitalization due to pneumonia decreased from 0.58 to 0.05 per patient per year (P=0.08) and the immunoglobulin G level (mean+/-S.D.) changed from 66.2+/-63.9 (range: 0-210 mg dl(-1)) to 552.4+/-199.1 (range: 136-942 mg dl(-1)) (P<0.001). Treatment of agammaglobulinemia with IVIG significantly reduced the incidence of pneumonia and hospital admission. Intensive management and regular monitoring is required in order to fully prevent severe respiratory complications.