A workshop on transfer factor, sponsored by the Immunology, Allergic and Immunologic Diseases Program of the National Institute of Allergy and Infectious Diseases, National Institutes of Health, was held in Bethesda, Maryland, on February 25, 1981. The purpose of the meeting was two-fold: (1) to review the state of the art of transfer factor and (2) to suggest future directions for research in this area, specifically in regard to the prophylactic use of transfer factor for varicella-zoster in leukemic children.