The complete nucleotide sequence of the gene encoding the matrix protein (M) of the porcine paramyxovirus LPMV has been determined. The gene is 1376 nucleotides long including 5' and 3' non-coding sequences with a protein-coding sequence of 1107 nucleotides. The deduced protein, containing 369 amino acids with a calculated Mr of 41,657, is hydrophobic overall with a net positive charge of +17.5. Comparative sequence analysis revealed high amino acid homology to other paramyxovirus M proteins, with the highest degree of identity (46%) with the human mumps virus. This is strong evidence that the porcine paramyxovirus LPMV is a genuine member of the paramyxovirus genus.