A chimeric gene encoding the alfalfa mosaic virus (AlMV) coat protein was constructed and introduced into tobacco and tomato plants using Ti plasmid-derived plant transformation vectors. The progeny of the self-fertilized transgenic plants were significantly delayed in symptom development and in some cases completely escaped infection after inoculated with AIMV. The inoculated leaves of the transgenic plants had significantly reduced numbers of lesions and accumulated substantially lower amounts of coat protein due to virus replication than the control plants. These results show that high level expression of the chineric viral coat protein gene confers protection against AIMV, which differs from other plant viruses in morphology, genome structure, gene expression strategy and early steps in viral replication. Based on our results with AIMV and those reported earlier for tobacco mosaic virus, it appears that genetically engineered crossprotection may be a general method for preventing viral disease in plants.