Twenty-one patients with primary humoral immunodeficiency were treated for 1 year with a chemically intact immunoglobulin, 300 mg/kg body weight given intravenously every 3 weeks, to compare immunoglobulin levels and clinical status with results achieved after standard treatment with intramuscular immunoglobulin given previously for 1 year. A substantial reduction of specific acute illnesses and antibiotic use was found for 18 of the 21 patients, particularly during the second 6 months of treatment. Average IgG levels before intravenous infusion were increased 243 mg/dL over previous intramuscular pre-injection levels. Adverse effects were recorded for 2.5% of infusions.