Potato varieties Russet Burbank and Ranger Russet were transformed with a cDNA version of the 23 kD coat protein cistron (CP) of the potato leafroll virus (PLRV) using anAgrobacterium-mediated procedure. Clones were assayed for presence of thenpt- II and CP genes by Southern analysis, for expression of CP mRNA by Northern analysis, and for presence of PLRV coat protein in uninoculated and aphid inoculated plants by ELISA and Western blot analysis in uninoculated plants. Two putative Russet Burbank transformants were escapes, lacking eithernptll or CP, while one putative Ranger Russet transformant possessed thenpt- II gene but not the CP gene. In Russet Burbank and Ranger Russet, some transformants had statistically lower virus titer. The lowered titer was consistent throughout assays at three times during primary infection and one assay of secondary infection. The ranking of virus titer across all tests was statistically consistent. Transformants with the lowest secondary titers had virus contents 15 and 31 % of the titers of untransformed controls for Russet Burbank and Ranger Russet, respectively. The virus titer of the two Russet Burbank escapes and the Ranger Russet with only thenpt- II gene did not differ significantly from their respective untransformed controls.