A simple assembly for paper electrophoresis and its optimal working conditions are described. The construction of a simple densitometer is also briefly presented.In using the scanning method, azocarmin B was found to be a suitable dye for the quantitative determination of the relative amount of serum protein fractions, as checked by nitrogen determination with the micro-Kjehdahl method. It was found, that no correction factor was necessary for the globulin fractions.Reproducibility of the method is considered satisfactory.The electrophoretic values of sixty normal human sera and a number of patients' sera are reported.