An in situ hybridisation technique, based on oligodeoxynucleotide probes and tyramide signal amplification, is described for the detection of foot and mouth disease virus RNA in infected cells. Biotinylated oligodeoxynucleotide probes, with and without tyramide signal amplification, were compared. The tyramide signal amplification detection enhances by at least 100-fold the sensitivity of in situ hybridisation.