The infective RNA of the calicivirus, vesicular exanthema virus, has been shown to contain a protein which is apparently linked to the RNA by a covalent bond. The protein remained bound to the RNA after boiling with SDS-mercaptoethanol-urea or treating with formamide-dimethylsulphoxide but was removed by incubating with proteinase K. The mol. wt. of the protein was estimated to be about 1o X 1O(3) by electrophoresis in highly cross-linked polyacrylamide gels. The infectivity of the RNA was destroyed by removal of the protein with proteinase K.