Infection is a frequent cause of morbidity and mortality in patients with chronic lymphocytic leukaemia (CLL) and low-grade B cell lymphomas. Several factors may contribute to an increased risk of infection in individual patients but, overall, impaired antibody production--commonly manifest as hypogammaglobulinaemia--appears to be a major factor. Early studies of immunoglobulin replacement using the intramuscular route showed equivocal results. More recently, highly purified preparations of IgG have become available for intravenous use making regular replacement therapy a realistic possibility for patients at risk. We have recently undertaken a multi-centre, randomized, double-blind, placebo-controlled study of regular intravenous immunoglobulin (IVIg) replacement in patients with CLL at risk of infection as defined by presence of hypogammaglobulinaemia, a significant infection history, or both. Eighty-four patients with CLL were randomized to receive IVIg (Gammagard Baxter Healthcare Corporation Hyland Division), 400 mg/kg body weight or an equivalent volume of normal saline every 3 weeks for a year. Patients receiving IVIg showed a 45% reduction in bacterial infection during the study period (p = 0.01). In patients completing a full year of study, a 61% reduction in bacterial infection was observed (p = 0.001). A significant reduction in bacterial infection was also seen in a blinded crossover study in which 12 patients from one centre who had completed a full year in the former study were subsequently given the alternative infusion for a further year. The incidence of serious bacterial infection was significantly less during the months in which patients received IVIg compared with placebo (p = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)