A simple modification of high resolution electrophoresis on supported cellulose acetate is described. This modification is made by adding the surfactant Tween 20 to the buffer and permits the identification of apolipoproteins A-I and B as well as the usually detected serum proteins. The procedure is reproducible using various supported cellulose acetate plates with manual and automated procedures. Furthermore, this improved high resolution electrophoresis allows the semiquantitative evaluation of these apolipoproteins both on freshly collected and on -20 degrees C stored serum samples.