Following administration of uranium parenterally into rats in an acute dose, the increase in protein excretion consisted not only of an increase in the normally occurring albumin but to a greater extent an increase in the various globulins. At the height of proteinuria, the electrophoretic pattern of the excreted proteins strongly resembled the pattern of the serum proteins. The appearance of these serum-like urinary proteins suggests a defect in the glomerulus filtration apparatus and provides further evidence that the glomerulus, as well as the tubule, is altered by uranium administration.