3. The subject has been receiving licensed or investigational (Phase III or IIIb) immunoglobulin intravenous (IGIV) replacement therapy at a dose that has not changed by + 50% of the mean dose for at least 3 months before study entry and is between 300 and 800 mg/kg/infusion. The infusion interval must be between 21 and 28 days inclusive. The subject must have maintained a trough level at least 300 mg/dL (milligram per decilitre) above baseline serum IgG levels (defined as before initiation of any gamma globulin treatment for that subject). The trough level must be 600 mg/dL.