The electrophoretic patterns of a series of normal and pathological human sera and plasmas have been obtained using the schlieren scanning method. From these patterns the mobilities and concentrations of the electrophoretically distinct protein components have been computed. The mobilities fall into five well defined groups corresponding to albumin, α, ß, and γ globulins, and fibrinogen. The concentrations of the different components in pathological sera have been compared with those in normal sera, and the following tentative generalizations may be made. The albumin/globulin ratios for pathological sera have been consistently lower than those for normal sera. The values of the α globulin/albumin ratio for the sera of the febrile patients studied were high, the average value being over twice the normal value. The γ globulin/albumin ratios for aplastic anemia and rheumatic fever sera were also above normal. Certain pathological conditions, notably nephrosis, were accompanied by large increases in a γ globulin. There is evidence that, in part at least, this consists of a labile lipo-protein.