The transfer factor (TF) was described in 1955 by S. Lawrence. In 1992 Kirkpatrick characterized the specific TF at molecular level. The TF is constituted by a group of numerous molecules, of low molecular weight, from 1.0 to 6.0 kDa. The 5 kDa fraction corresponds to the TF specific to antigens. There are a number of publications about the clinical indications of the TF for diverse diseases, in particular those where the cellular immune response is compromised or in those where there is a deficient regulation of the immune response. In this article we present our clinical and basic experiences, especially regarding the indications, usage and dosage of the TF. Our group demonstrated that the TF increases the expression of IFN-gamma and RANTES, while decreases the expression of osteopontine. Using animal models we have worked with M. tuberculosis, and with a model of glioma with good therapeutic results. In the clinical setting we have worked with herpes zoster, herpes simplex type I, herpetic keratitis, atopic dermatitis, osteosarcoma, tuberculosis, asthma, post-herpetic neuritis, anergic coccidioidomycosis, leishmaniasis, toxoplasmosis, mucocutaneous candidiasis, pediatric infections produced by diverse pathogen germs, sinusitis, pharyngitis, and otits media. All of these diseases were studied through protocols which main goals were to study the therapeutic effects of the TF, and to establish in a systematic way diverse dosage schema and time for treatment to guide the prescription of the TF.