Rinderpest (RP) is a viral disease of ruminants with > 95% morbidity and mortality. We have cloned the cDNA of the nucleocapsid (N) gene of the virulent Kabete O strain of rinderpest virus (RPVK) and compared its nucleotide and deduced amino acid sequences with those of the N genes of the lapinized strain of rinderpest virus (RPVL), measles virus (MV), and canine distemper virus (CDV). The gene has an open reading frame of 1575 nucleotides and encodes a protein of 525 amino acids with a molecular weight of 59 kDa. The nucleotide sequence of the coding region of the N gene of RPVK is 88.6, 68.9, and 63.2% homologous with N genes of RPVL, MV, and CDV, respectively. We have developed a recombinant baculovirus that expresses the N protein (rRVN) of RPVK in insect cells (Sf9) and larvae (Spodoptera frugiperda). rRVN was used as a coating antigen in an ELISA to distinguish vaccinated animals from those infected with RPV and was also used successfully in the diagnosis of two other morbilliviruses, MV and peste des petits ruminants (PPRV). Crude lysate of a single infected larva (0.2-0.3 g) was sufficient to coat 150 ELISA plates for serological diagnosis of 7200 serum samples in duplicate.