Forty-two patients with chronic lymphocytic leukaemia (CLL), serum IgG levels < 5.5 milligrams and a history of two or more recent infections, were randomized to receive infusions of 18 g human intravenous immunoglobulin (IVIg) or human albumin placebo every three weeks. During the 12 month study 122 infections were documented but only four were associated with neutropenia. Ten patients (24%) with IgG levels < 3.0 milligrams experienced 65% of the infections. In response to IVIg there were immediate and accumulative increases in serum IgG levels and an associated decrease in total and serious infections. If three further infections occurred, placebo patients were commenced on 18 g IVIg, and IVIg patients were increased to 24 g IVIg. Approximately 50% of these cases subsequently remained infection free. The study shows the usefulness of prophylactic Sandoglobulin in CLL patients with hypogammaglobulinaemia, and suggests that this may be justified in those with recurrent infections and serum IgG levels < 3 milligrams.