It has recently been shown that cowpea plants can be infected with a cowpea mosaic virus (CPMV) chimera containing an antigenic site from foot-and-mouth disease virus (Usha et al., Virology 197, 366-374, 1993). Analysis of progeny RNA produced during such an infection has revealed that the inserted sequence is rapidly lost during serial passaging, probably by a process of homologous recombination. Using the information gained from this analysis, we have redesigned the chimeras in such a way that they are now genetically stable. The modified constructs have been used to obtain large quantities of purified virus particles expressing epitopes derived from human rhinovirus 14 (HRV-14) and human immunodeficiency virus type 1 (HIV-1). The chimeric virus particles possess the antigenic properties of the inserted sequence and, in the case of the HRV-14-derived construct, it has been shown that the inserted epitope is immunogenic in rabbits. These results demonstrate that CPMV can be used as a high-yielding system for the presentation of foreign peptide sequences.