DMSO has multiple known pharmacological properties. In addition to those referred to include: cryoprotective action, radioprotective effect, influence on serum cholesterol in experimental hypercholesteremia, and platelet aggregation antagonism. How the multiple properties of this chemical affect therapy in clinical medicine must yet be explained. It is clear, however, that DMSO does affect biological systems, and that this influence has many clinical applications. Perhaps one of the most interesting and significant properties of DMSO is its ability to move other drugsthrough membranes. When mixed with DMSO, many drugs appear to be potentiated in their physiologic effect; thus smaller doses are required and less toxicity is demonstrated. In cancer chemotherapy, this value already has practical use. Some of the studies to be reported in this monograph will describe additional, almost unbelievable observations. Perhaps the mechanism of action of these clinical phenomena will be found in one or more of the pharmacological properties described. It would not be surprising, however, if we were to conclude with a resolution to search for new explantations of the mystery of DMSO, for it would appear that DMSO is really a new principle in medicine and cannot always be measured by existing standards.