The authors report a female patient with congenital pulmonary alveolar proteinosis (PAP). She had two brothers who died from the same disease. BAL did not improve her progressive respiratory failure. After intravenous immunoglobulin G (IVIG) administration for complicated hypogammaglobulinemia, she recovered from respiratory failure. The efficacy of IVIG was confirmed by recovery from deterioration in respiratory status and improvement in chest CT findings on two separate occasions. Subsequently, the patient remains free from respiratory symptoms for more than 3 years on an ongoing regimen of monthly IVIG. She had no surfactant protein (SP) B deficiency. Alveolar macrophages (AM) obtained from her BAL fluid were small and showed decreased phagocytotic activity. Immunostaining revealed weak expression of PU.1 in her AM, a key protein in AM maturation. All nucleotide sequences of granulocyte-macrophage colony stimulating factor (GM-CSF), GM-CSF-receptor and PU.1 were normal. Endotoxin-induced GM-CSF release from peripheral mononuclear cells (PMNC), and proliferation of PMNC in response to GM-CSF were normal. In addition, an antibody against GM-CSF, as seen in adult patients with idiopathic PAP, was not detected in the serum or BAL fluid. Although the patient's PMNC secreted only small amounts of IgG and IgM, an EB virus-derived cell line of her B cells secreted IgM as much as normal control cells. In a flow cytometric study, IgM was expressed on the cell surface. In conclusion, an abnormality in a single gene may have decreased secretion of immunoglobulin from the B cells and the AM phagocytotic activity in the patient.