Wild measles virus isolated in a marmoset lymphoblastoid B95a cell line induced rashes and Koplik's spots when inoculated parenterally in cynomolgus and squirrel monkeys. Marked leukopenia. associated with transient decrease in the CD4(+)-to-CD8+ T-cell ratio also was induced. Virus growth, as well as histologic lesions of necrosis and giant cell formation, was observed in the lymphoid tissues. Thus clinical signs of acute measles were successfully induced in monkeys by inoculation with cell-culture-grown measles virus. These nonhuman primate models of measles will be useful for study of the pathogenesis of acute measles virus infection in terms of generalized clinical signs of disease, leukopenia, and changes in the lymphocyte subsets.