The concentration and immunoelectrophoretic properties of the 19S and 7S immunoglobulins were determined in the sera of normal, lymphoid tumor-bearing, and immunized Xenopus laevis. We found that normal X. laevis possessed a higher level of 19S (186 mg/100 ml) than of 7S (68 mg/100 ml) Ig. The concentration of these proteins is significantly increased in the sera of immunized animals. Xenopus with spontaneous lymphoid tumors had a significantly increased concentration of 19S Ig. This increase was characterized in immunoelectrophoreses by the appearance of a new bow of precipitation, in addition to the usual curve.