For centuries it has been the dream of many physicians to cure illnesses by eliminating disease provoking substances which are thought to circulate in the human body. Technical developments during the past 20 years have made therapeutic plasma exchange (TP) a useful procedure for clinical application. Because of the lack of well controlled studies the true benefit of the method remains speculative in many clinical situations. Since the report of the American Medical Association (AMA) Panel on Therapeutic Plasmapheresis in 1985 several controlled studies on this subject have been published in recent literature; they are reviewed in this article. In summary, TP seems justified only in some area and well defined situations such as thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, acute and severe myasthenia gravis, severe Guillain-Barré-syndrome, hyperviscosity syndromes such as hyper- and paraproteinemia, and in several intoxications and metabolic disorders such as Refsum disease or hereditary hyperlipidemia type IIa.