The antiviral activity of antisense oligonucleotides corresponding to different regions of foot-and-mouth disease virus (FMDV) genome has been assessed in BHK-21 cells. The locations of the oligonucleotides used were: (i) two regions within the internal ribosome entry site (IRES), involved in the regulation of the translation initiation of the viral polyprotein; (ii) each of the two functional initiator AUGs; (iii) an internal sequence of P2A gene; and (iv) a region at the 3' end non-coding region. Cytoplasmic microinjection of oligodeoxyribonucleotides and oligoribonucleotides complementary to the second AUG resulted in a transient inhibition of viral VP1 expression in infected cells. Significant inhibitions, ranging from 35 to 52%, were obtained at 5 h post-infection using oligonucleotide concentrations of 125 microM and higher. The extent and duration of this inhibition seemed to be mediated by both a rapid transport to the nucleus and the short half-life of the oligonucleotide. This inhibition of FMDV protein synthesis was correlated with a reduction of virus yield of about 50%, as observed after the addition to the cell culture of an oligodeoxyribonucleotide phosphorothioate complementary to the second AUG.