A reverse transcription-polymerase chain reaction (RT-PCR) has been developed for the cloning of coat protein-encoding genes (CP) of cymbidium mosaic virus (CyMV) isolated from three different infected species of Thai orchid: Cattleya, Mokara and Oncidium. The analysis of the compiled sequences of the cDNA clones shows a single open reading frame which encoded a CyMV CP gene. The gene is 669 nucleotides (nt) long and codes for a 23 761-Da protein. The nt sequences of CyMV CP from the Thai isolates showed that some of them differ at a single nt and share 97% homology, but all of them share only 88% homology to the Singapore Oncidium isolate. In addition, the CyMV CP, unlike that from other potexviruses, is distinctive and differs greatly from the amino acid composition deduced from the nt sequence of the CP.