The distribution of mumps virus in 1 experimentally infected monkey 96 hrs. after the installation of mumps virus into Stensen''s ducts was investigated by the simultaneous use of 2 methods. The antigens of mumps virus were sought in frozen sections of various organs by means of fluorescein-labelled antibody and observation under the fluorescence microscope. After the prepn. of the sections, the same blocks were ground and injected into embryonated hen''s eggs as a test of infectivity. The results furnished by the 2 methods were in fair agreement. Virus was demonstrated in the brain and spinal cord as well as in both parotid glands, although the animal had shown no neurological signs. No virus was demonstrated in the other organs examined.