Abstract A simple rapid method is described for concentrating urine and other biological fluids for protein electrophoresis. No extra equipment is necessary and the method could readily be carried out in any routine laboratory. The method is superior to those which have been described in the literature and satisfactory electropherograms on cellulose acetate membrane filter can be obtained after 5 ml of a dilute solution is concentrated 4–5-fold for 90–120 min by dialysis against powdered sucrose. Electrophoresis and quantitation of proteins indicate that no alteration of the proteins occurred by this concentration procedure. The entire procedure including the electrophoresis requires not more than 3 1 2 h and several specimens can be concentrated at one time.