bAn amino acid consensus sequence for the seven serotypes of foot-and-mouth disease virus (FMDV) nonstructural protein 3B, including all three contiguous repeats, and its use in the development of a pan-serotype diagnostic test for all seven FMDV serotypes are described. The amino acid consensus sequence of the 3B protein was determined from a multiple-sequence alignment of 125 sequences of 3B. The consensus 3B (c3B) protein was expressed as a soluble recombinant fusion protein with maltosebinding protein (MBP) using a bacterial expression system and was affinity purified using amylose resin. The MBP-c3B protein was used as the antigen in the development of a competition enzyme-linked immunosorbent assay (cELISA) for detection of anti-3B antibodies in bovine sera. The comparative diagnostic sensitivity and specificity at 47% inhibition were estimated to be 87.22% and 93.15%, respectively. Reactivity of c3B with bovine sera representing the seven FMDV serotypes demonstrated the pan-serotype diagnostic capability of this bioreagent. The consensus antigen and competition ELISA are described here as candidates for a pan-serotype diagnostic test for FMDV infection. Foot-and-mouth disease (FMD) is the most contagious viral vesicular disease that affects cloven-hoofed livestock species. FMD has significant global socioeconomic consequences, from national livestock industries suffering because of international trade restrictions to subsistence farmers suffering because of losses of stock productivity and livelihoods. Western European, North American, and Far East Asian/Pacific regions and most South American countries have official recognition of freedom-from-FMD status, with or without vaccination, by the World Organization for Animal Health (OIE). Regions in which FMD remains endemic tend to be those of lesser economic capacity, and this limits their ability to control or to eradicate the disease (1, 2). As a result, FMD remains an ongoing problem in regions in which it is endemic, and it is a persistent threat to regions that are free of the disease. Seven serotypes have been described for foot-and-mouth disease virus (FMDV), i.e., O, A, C, Asia 1, and South African Territories 1 (SAT1), SAT2, and SAT3. The disease forms produced by each serotype are clinically indistinguishable (3); similarly, FMD is clinically indistinguishable from other vesicular lesion-causing diseases, such as vesicular stomatitis, swine vesicular exanthema, and swine vesicular disease, and laboratory-based clinical diagnosis is required (4, 5). FMD infections may be mild or subclinical in ovine or caprine species, further complicating clinical diagnosis (6, 7). Exposure to one serotype does not confer cross-serotype immunity, potentially complicating diagnosis when multiple serotypes are circulating during an outbreak (8). A definitive diagnosis of FMD is possible only with laboratory testing.Conventional serological assays for FMD, including the virus neutralization test, liquid-phase blocking enzyme-linked immunosorbent assay (ELISA), and so...