Electrochemical experiments were performed in dimethylsulfoxide (DMSO)-electrolyte systems below their freezing points. The microelectrode experiments showed that sigmoidal-shaped curves can be obtained with values of E(3/4) - E(1/4) close to theoretical values for a reversible reaction at temperatures below the system freezing point. This indicates a change in mass transport mechanism from diffusion control to a surface confined process if the temperature is decreased further. The differential scanning calorimetry results, together with previous electron spin resonance experiments, confirm the existence of a liquid microphase. A modified theoretical model is suggested. Similar electrochemical responses were also obtained in DMSO-H2O-electrolyte systems studied for liquid effect injury. It is shown that electrochemical methods can be used as a tool to characterize the physical and chemical properties of these DMSO mixture systems below their freezing points. The existence of a DMSO liquid microphase may be one reason why liquid effect injury to biological materials is reduced at low temperature. The application of electrochemical methods in optimizing the components of cryopreservation systems is discussed.