The cDNA coding sequence of the RNA-dependent RNA polymerase (3Dpol) of Mengovirus was cloned and expressed in a bacterial system. Eleven monoclonal antibodies were raised against the recombinant Mengo 3Dpol (rM3D). All of them recognized the recombinant and the viral-induced form of the protein. The panel of monoclonals belonged to the IgG1 and IgG2a isotypes and were mapped to four different epitopes in the 3D molecule by competition assays. All monoclonals recognized Mengo 3Dpol in western blots and cross-reacted with the homologous polymerases of seven other cardioviruses but failed to react with 3Dpol from poliovirus type 1 and 3 or rhinovirus type 14 and 16.