Pseudomonas aeruginosa continues to be a common lethal pathogen in burned patients. Active and passive immunization represents an important therapeutic adjunct. Ten patients with Pseudomonas sepsis, eight with bacteremia, were passively immunized with tetravalent hyperimmune Pseudomonas-intravenous immunoglobulin G. The dose was 500 mg/kg given on two successive days. The IgG levels rose after infusions and were maintained in the normal range throughout the septic course. Antibodies to the immunotype of each of the Pseudomonas responsible for the bacteremias were present in the hyperimmune globulin. Clinical improvement in the patients was associated with a 3- to 125-fold postinfusion increase in antibody titers. Seventy per cent of the patients survived, including six of the seven with bacteremia.