A new method for the purification of apolipoprotein H by affinity chromatography followed by continuous-elution electrophoresis is described. It is both simpler and less complicated than the chromatographic and electrophoretic methods usually used. In addition, apolipoprotein H is isolated in a pure, structurally uncleaved form. This is of importance, as impairment has been detected in commercial preparations. The separation and purification of apolipoprotein H is a necessary prelude to its quantitative determination and phenotyping, and hence the clarification of its physiopathological mechanisms in lipid metabolism.