We have cloned and sequenced the entire M gene of the vaccine strain of rinderpest virus and that of the virulent Kabete ''O'' strain from which it was derived. The sequences of these two genes are essentially identical (99% at the nucleotide level), but were very different from a previously published Kabete O M gene sequence (M. Lime and T. Yilma, 1990, Virology 175, 323-327). Inspection of the nucleotide and deduced amino acid sequences of known morbillivirus M genes showed that the earlier sequence was clearly from a morbillivirus, but neither from rinderpest virus nor from peste des petits ruminants virus. (C) 1994 Academic Press, Inc.