We have investigated the bovine immune response to heterologous proteins expressed using a recombinant rinderpest virus (RPV). A new gene unit was created in a cDNA copy of the genome of the vaccine strain of RPV, and an open reading frame inserted that encodes the polymerase (3Dpol) and parts of the capsid protein VP1 from foot-and-mouth disease virus (FMDV). Infectious recombinant RPV was rescued and shown to express the FMDV-derived protein at good levels in infected cells. The rescued virus was only slightly more attenuated in tissue culture than the original virus. Cattle infected with this recombinant generated a normal immune response to RPV, and were protected from lethal challenge by that virus. Experimental animals showed a specific delayed-type hypersensitivity response to FMDV 3Dpol, similar to that seen in FMDV infection; however, no antibodies were detected recognizing either of the components of the FMDV-derived protein, nor was any proliferative response to these epitopes found in isolated peripheral blood lymphocytes from infected animals. No protection was seen against FMDV infection.