We introduced replicase genes of brome mosaic virus (BMV) to Nicotiana tabacum cv. Petit Habana (SRI) using two different types of transformation vectors containing cDNAs of BMV RNA 1 and RNA 2. One type (V type) contains cDNA from which complete viral RNAs are transcribed. These RNAs can function as templates for viral replicase. The other type (M type) contains cDNA from which viral RNAs without their 3' non-coding regions are transcribed; these RNAs can only function as mRNA. Viral replicase expressed from the integrated cDNAs in both V and M type transgenic plants can complement an infection by BMV RNA 3.