Cucumber mosaic virus (CMV) and tomato aspermy virus (TAV) are closely related cucumoviruses. We have made pseudorecombinant viruses in which the RNAs 3 of these two viruses have been exchanged and recombinant viruses containing chimeric RNA 3 molecules, in which the coat proteins and the 3'-end regions of CMV and TAV have been exchanged, giving rise to recombinants designated RT3 and TR3. The replication properties and the cell-to-cell and long-distance movement patterns of these pseudorecombinant and recombinant viruses were examined in different hosts. All the viruses were able to replicate and accumulate RNA 4 in protoplasts. The pseudorecombinants and the R1R2RT3 recombinant infected tobacco systemically, but the R1R2TR3 recombinant was not detectable, even in the inoculated leaves. Comparison of the abilities of the viruses to replicate in protoplasts and intact cucumber plants suggests that cell-to-cell movement factors are also encoded by RNAs 1 and/or 2. Major determinants of symptom severity in Nicotiana glutinosa are localized on the 3' part of RNA 3, and in Nicotiana benthamiana, more severe symptoms were observed with the T1T2R3 strain than with the others tested.