The safety and patient acceptance of two preparations of modified (reduced and alkylated) immune globulin for intravenous use were evaluated; one preparation was formulated as a 5% solution in 10% maltose (IGIV-maltose), the other did not contain maltose (IGIV). In this double-blind trial each of 29 immunodeficient patients received three consecutive monthly infusions (100 or 150 mg/kg immune globulin) of one preparation before being crossed over to the other. Only 3 of 29 patients had adverse reactions when on IGIV-maltose, compared with 22 who had side-effects during infusions of IGIV (p < 0.001). Adverse reactions were recorded during 3 of 87 IGIV-maltose infusions and during 51 infusions with the maltose-free IGIV (p < 0.001). 27 patients expressed preference for IGIV-maltose. IGIV-maltose seems safe and will permit rapid infusion of large doses of immune globulin, thus improving the management of patients with antibody deficiency diseases.