Transgenic Burley line 2RC-6.13 expresses an untranslatable mRNA containing the tobacco etch virus (TEV) coat protein open reading frame and exhibits complete TEV resistance. This line has three transgene inserts in two linkage groups. 2RC-6.13 was hybridized with susceptible BU 49, and homozygous lines with 0, 2, 4 and 6 copies of the transgene were produced and hybridized in all combinations. Lines or hybrids with 4 or more copies of the gene expressed complete resistance, but had a low steady state concentration of the transcript. Plants with 1 or 2 copies of the gene were initially susceptible but recovered, and had a high transcript concentration. Virus resistance was associated with post-transcriptional regulation of the transcript. Using 35S promoters, multiple copies of transgenes will generally be required for complete resistance to a virus.