Today's statement of transfer factor, an immunostimulator derived from leukocytes which enhances antiinfectious immunity, is observed in the review. Basic biological, physical and chemical characteristics of the transfer factor, its possible action mechanisms, and laboratory and clinical methods of use to cure infectious fungal (Candida, Coccidium), invasive (schistosomiasis, leishmaniasis, cryptosporidiosis), viral (varicella zoster, ophthalmic herpes, Herpes simplex types 1 and 2, H. zoster, H. simplex ceratitis, genital herpes, human herpes virus type 6, postherpetic neuritis, hepatitis B, AIDS), and bacterial infections (Mycobacterium leprae, M. tuberculosis, M. fortuitum, Salmonella cholerae suis, S. dublin, S. Virchov, Brucella abortus, Actinobacillus pleuropneumoniae, bacterial sepsis, Staphylococcus) are described.