The electrochromatography column is a unique glass device designed to function both as a chromatography column and as an electrophoresis column; it can also be operated so that both column chromatography and electrophoresis can take place in one simultaneous operation (electrochromatography). When the column is used for electrochromatography, proteins of the same molecular size, but with different electrophoretic mobilities, will be separated by electrophoresis, whereas proteins with the same electrophoretic mobilities but of different molecular size will be separated by molecular sieving. If proteins vary only slightly in these physical properties, separation is greatly enhanced by the action of the electric field on the filtering molecules. Thus, electrochromatography allows proteins to be separated simply, rapidly, and with greater resolution than other systems currently available. Electrochromatography has been used successfully for the purification of hepatitis B antigen, which is not separated from closely related serum immunoglobulins by either chromatography or electrophoresis. This method may become an important tool for the isolation and purification of a large number of proteins and viruses not easily separated by means of current technology.