The proteins induced by infection of BHK 21 cells with foot-and-mouth disease virus have been compared by tryptic peptide analysis. The results indicate that there are three primary products 5'--P88, P52, P100--3'. The polypeptide P56, which we considered previously to be a primary product, is derived from the region of the genome that codes for P100. The results indicate that there are alternative cleavage pathways of P100, the polypeptide coded for by the 3' end of the genome.