An immunocapture ELISA for the diagnosis of rinderpest and peste des petits ruminants is described. Monoclonal antibodies directed against non-overlapping antigenic domains on the nucleocapsid (N) were used to detect the virus N protein in supernatants from infected cells and in field specimens. The assay, which is very sensitive, can be performed in one hour on pre-coated plates. There was no cross reaction between the two viruses in the test and the N protein could be detected in infected cell supernatants kept at ambient temperature for one week. These results show that the ELISA is suitable for routine diagnosis of field samples.