To review our policy of prophylactic treatment with intravenous immunoglobulin (i.v.IG) in chronic lymphocytic leukemia (CLL), we analyzed the infection history, serum IgG levels (S-IgG) and disease stage of 146 patients who were treated and followed at our institution in 1980-1989. S-IgG was available for 98 patients: 55% were hypogammaglobulinemic and 56% had had at least one severe infection. There were significant associations between S-IgG and the occurrence of infections (p less than 0.01) and disease stage (p less than 0.02). There was also a significant association between disease stage and occurrence of infections (p less than 0.001). Severe infections tended to accumulate in patients with subnormal S-IgG and advanced disease stage. Totally, 292 infections were recorded, and the incidence of moderate to severe infections was 0.47 per patient year. Infection mortality was high: 42 patients died of a severe infection (46% of all causes of death). Patients with a low S-IgG and advanced disease stage are the most susceptible to death from infection and would be most likely to benefit most from i.v.IG prophylaxis; however, the cost of this therapy is so high that strict individual consideration still remains crucial for treatment decisions.