Polarographically active sulfur was distributed among the serum-protein fractions as follows (in percentages): albumin, 63.21; α1-globulin, 3.17; α2-globulin, 7.92; β-globulin, 14.54; α-globulin, 11.16. The results compare well with those obtained by X-ray spectrometry. The same method was applied to sera from patients suffering from malignant processes and some other diseases; the percentage of polarographically active sulfur in fractions of plasma from diseased individuals varied considerably.