NOTES 1069 acetate and lead citrate, and examined under a JEOL 100 C electron microscope. Both giant cells and virus antigens were found in the thymus, lymph nodes, spleen, and trachea, but not in the other organs. The giant cells, which consisted of both reticular and lymphoid cells (Fig. 1), were widely distributed in the lymphoid tissues, particularly in the germinal center. In the trachea, giant cells were found in the epithelium. These giant cells in the monkeys were histopathologically similar to those reported previously (7, 10, 13). The synthesis of viral proteins in the trachea, spleen and mesenteric lymph nodes was compared by the indirect IF technique using monoclonal anti-measles virus antibodies. In the trachea, positive reactions were obtained with all the mono-