Four primary cleavage products, mol. wt. 10(3) X 100, 88, 56 and 52 (P100, P85, P56 and P52 respectively) are present in BHK 2I cells infected with foot-and-mouth disease virus (FMDV). However, no precursor polyprotein equal to the sum of their mol. wt. was detected, even when amino acid analogues and proteolytic enzyme inhibitors were used. Three of the primary products were shown to cleave to smaller polypeptides, including the capsid polypeptides of the virus. Polypeptide P88, which was shown to be the precursor of the capsid polypeptides, is translated from the gene located at the 5'-end of the genome. The order of the structural polypeptides, determined by the use of emetine, is VP4, VP2, VP3, VP1. The order of the remaining primary cleavage products is P52, P56 and P100. P56 is a stable product, identical with the virus infection associated (VIA) antigen found in virus harvests. The function of the other two products P52 and P100 is not known. EMDV thus differs from other picornaviruses in that there is an extra primary cleavage product, apparently resulting from translation of more of the virus genome.