A paramyxovirus was isolated from cerebrospinal fluid of a dog with a history of incoordination and posterior paresis. The virus apparently was not related to canine distemper virus (CDV), considering the lack of virus neutralization with CDV-specific antibody, negative immunofluorescence with CDV-specific conjugate, and avirulence for ferrets. The virus was antigenically related to a prototype strain of canine parainfluenza virus, as determined by positive immunofluorescence with canine parainfluenza virus-specific conjugate and virus neutralization tests.