Serum and cerebrospinal fluid from multiple sclerosis (MS) patients and control subjects were tested and compared for presence and titer of neutralizing antibody against the most common canine viruses. Canine viruses included canine distemper virus (CDV), canine adenovirus 1 (CAV-1), canine parainfluenza virus (CPIV), canine herpesvirus (CHV), canine coronavirus (CCV), and canine parvovirus (CPV). Neutralizing titers against measles virus (MV) and human adenovirus 8 (HA8) were also tested. Significantly elevated (p less than 0.05) antibody levels in sera from MS patients were found only against MV and CDV, but this depended upon the study population and the method of evaluation. The CDV-neutralizing component in serum could be absorbed on MV-infected cells. Results of this study failed to establish a link between canine viruses and MS.