The distribution of surface immunoglobulin (Ig) determinants on Xenopus laevis splenic lymphocytes after combination with divalent rabbit anti-Ig coupled to ferritin was studied. The electron micrographs showed the presence of immune complexes in 67% of lymphocytes treated at 0 degrees C-4 degrees C. The complexes were located all around the membrane and uniformly distributed in a random fashion. The variation of ferritin grain counts on cell sections is such, that the existence of two major subclasses of Ig-positive cells may be suggested. Raising the temperature produced a rapid interiorization of the complexes in vesicles without any previous aggregation to form a "cap" having occurred.