Abstract Serum samples from 28 patients with macroamylasemia were studied by paper electrophoresis. Amylase activity appeared as a single peak located between the γand β-globulin zones and did not differ appreciably from normal serum amylase in electrophoretic mobility. When segments of the electrophoretic paper strip showing amylase activity were eluted and the eluate examined by dextran gel chromatography, the single peak was found to contain both a macroamylase component and the amylase of normal molecular weight. The ratio of macroamylase to amylase of normal molecular weight differed to a variable degree, however, from that in the untreated whole serum. Although the mechanism responsible for this change in ratio is not clear, it is possible that the macroamylase complex was partially dissociated by the electric field.