RNA transcripts were prepared from plasmids encoding an infectious cDNA of foot-and-mouth disease virus (FMDV) or derivatives in which the leader (Lab and Lb) and capsid protein coding sequences were deleted or replaced by sequences encoding chloramphenicol acetyltransferase (CAT). The transcripts were electroporated into BHK cells and the expression of CAT and the FMDV 3C protease was monitored. Detection of CAT and 3C was dependent on the ability of the transcript to replicate. All of the Lb coding sequence and 94% of P1 (the capsid protein precursor) coding sequence could be deleted without any apparent effect on the ability of the RNA to replicate. Thus, no cis-acting replication element is present within this region of the FMDV genome. Trans-encapsidation of these FMDV replicons was very inefficient, which may explain the lack of production of defective-interfering particles in FMDV-infected cells.