Cowpea mosaic virus (CPMV) is a bipartite RNA plant virus which has proved to be useful both for epitope presentation and as a polypeptide expression system. For epitope presentation, short antigenic sequences are expressed on the surface of the assembled virus. Chimaeric virus particles produced in this way can stimulate protective immunity in experimental animals. For polypeptide expression, we have created a vector in which foreign sequences can be inserted near the 3' end of RNA-2 and have successfully expressed a number of polypeptides in plant tissue. To extend the utility of the CPMV-based systems, we have recently developed a combined virus vector/transgenic expression system in which RNA-2 expressed from a transgene is replicated by RNA-1.