Serum obtained from trypan blue-treated rats showed an abnormal protein band between α-1 and α-2 globulin on paper electrophoresis, which could best be separated at pH 9.2. The compound appeared within one hour and was present for several days. The quantity of this material in serum was greater than that of α-2 globulin as short as 1 hour after trypan blue injection and seemed to increase with repeated injections of trypan blue. The compound was not formed in vitro by liver slices, erythrocytes or serum when incubated with trypan blue.