In a randomised cross-over study 12 patients with antibody deficiency and chronic lung disease received monthly infusions of either 0.6 g/kg or 0.2 g/kg intravenous immunoglobulin for six months, and were then switched to the alternative dose for a further six months. Although the incidence of infections did not differ greatly in the high-dose and low-dose phases, the frequency of acute infection was substantially reduced in those periods when serum IgG was 500 mg/dl or more. Pulmonary function worsened on the low-dose regimen and improved on the high-dose regimen.