60 children with acute lymphoblastic leukemia were sequentially randomized at the time of diagnosis: Immunoglobulin (Endobulin, Immuno) was administered intravenously to 30 patients at a dose 100 mg/kg/week during the first 3 months, followed by 2 x 200 mg/kg/month immunoglobulin during the 4., 5., 6. months. No immunoglobulin was administered to the control patients. We studied the effect of immunoglobulin prophylaxis on the number of days with fever, number of cases with bacteriologically proved infections, length and frequency of antibiotic therapy. Our data confirm the efficacy of immunoglobulin prophylaxis during the intensive phase of leukemia therapy in children.