Treatment with intensive myelosuppressive therapy results in decreased levels of immunoglobulins. Whereas pediatric cancer patients undergoing chemotherapy do not benefit from the routine administration of intravenous immunoglobulins, prophylactic intravenous immunoglobulins given after bone marrow transplantation or after peripheral stem cell transplantation reduce infectious complications. Still, prospective clinical trials are needed to define specific treatment groups who can benefit from immunoglobulin support. In addition, randomized studies are required to evaluate the proper dosage and duration of therapy. Passive immunization of children potentially incubated with varicella or measles is generally recommended.