The 2A region of the foot-and-mouth disease virus (FMDV) polyprotein is only 16 amino acids in length. During synthesis of the FMDV polyprotein a primary proteolytic processing event occurs between the 2A and 2B regions of the polyprotein. The activity responsible for this cleavage is not known but it is thought that either an unidentified virus-encoded proteinase may be responsible, or that 2A acts as a substrate for a host cell proteinase. A series of recombinant FMDV polyproteins has been constructed in which sequences to the N- or C-terminal side of the 2A region have been deleted. Analysis of the processing of these polyproteins shows that a 19 amino acid sequence spanning 2A is sufficient to mediate polyprotein cleavage at a site immediately C-terminal to 2A, whereas deletions extending into the 2A region prevent cleavage.