Monoclonal antibodies (Mabs) have long been considered a good class of natural drugs, both because they mimic their natural role in the body and because they have no inherent toxicity. Although rodent Mabs are readily generated, their widespread use as therapeutic agents has been hampered because they are recognized as foreign by the patient. Evidently, clinical Mabs should be as human as possible and results with some of the more recently developed chimerized and humanized Mabs are testimony to this. Mabs that are entirely human are now being produced from phage display and transgenic mice. The first fully human Mabs generated by phage display have already entered clinical trials, and together with recent advances in these technologies, may finally realize the full potential of antibodies.