The nucleoprotein (N) gene of Hendra virus (HeV), an unclassified member of subfamily Paramyxovirinae in the family Paramyxoviridae previously known as equine morbillivirus, was cloned and sequenced. The majority of the deduced amino acid sequence was further confirmed by direct sequencing of peptide fragments of the N protein derived from purified virions. The 3' untranslated sequence of the HeV N gene mRNA was 568 nt and was much longer than that observed in other Paramyxovirinae. The N protein was 532 amino acids in length with a molecular mass of 58.5 kDa. Although the HeV N protein had a slightly higher amino acid sequence identity to those of the genus Morbillivirus than to those of other Paramyxovirinae genera, the level of identity was much lower than that observed within the morbilliviruses. Our results indicated that HeV could not confidently be classified as a member of the genus Morbillivirus, Paramyxovirus or Rubulavirus and suggest that the virus be classified in a new genus within the Paramyxovirinae.