The sequences of a region of the nucleocapsid protein gene, between nucleotides 1231 and 1686, encoding the C-terminal 151 amino acid residues of the nucleocapsid protein have been determined for 16 strains of measles virus. Analysis of this region showed that it is highly divergent (up to 7.2% divergence in the nucleotide sequence and 10.6% divergence in the amino acid sequence between most distant strains) and that several lineages of measles virus can be found to co-circulate at a given time. Some of the lineages show geographical restriction. The results for measles virus are similar to those reported for other human paramyxoviruses such as mumps virus, parainfluenza type 3 virus and the avian Newcastle disease virus.