SummaryPlants of two potato cultivars were transformed with disarmedAgrobacterium rumefaciens(LBA4404) containing a binary expression vector. The vector contained sequences that encode the coat protein of potato leafroll luteovirus (PLRV) under the control of the 35s promoter of cauliflower mosaic virus. RNA transcripts from the integrated viral gene were readily detected in the transgenic plants. PLRV coat protein was detected in only some of these plants when using sensitive immunoblotting techniques. Tubers were collected from transgenic plants that became infected following inoculation either by viruliferous aphids or by grafting with scions from infected plants. When these tubers were used to grow plants with secondary infection, less virus accumulated in each plant of some transgenic lines than in control plants. The PLRV concentration, estimated at different sampling times, in plants of cv. Désirée (transgenic line B1) and cv. Pentland Squire (transgenic line C4) was about 15% and 30% respectively of that in control plants. Among a number of conventionally‐bred clones of potato, some were resistant to virus multiplication and were found to accumulate little virus. The coat protein‐mediated resistance in transgenic potato plants is discussed in relation to the conventional gene‐mediated resistance found in some breeding