IN the course of chromatography of proteins on UFS nitrocellulose membrane filters1, it was observed that the areas occupied by a relatively homogenous film of the firmly adsorbed serum proteins were approximately proportional to the concentration of the given sample. The best results were achieved when slightly acid buffers were used. The protein spots, however, had oblong and irregular shapes after one-dimensional chromatography, and an accurate quantitative determination of the areas was rather difficult and inconvenient, especially as a routine procedure.