To test the resistance of potato cultivars to potato leafroll luteovirus (PLRV) in the field, small plots each containing 3 rows of 3 plants of the same cultivar were planted next to a row of infector plants. Harvested tubers were tested for PLRV infection by enzyme-linked immunosorbent assay. Most of the PLRV spread (85%) was sequential rather than random (i.e. related to distance between test and infector plants). Twenty-six potato cultivars were screened for resistance to PLRV in 6 trials during 3 years at 3 locations. Summer, autumn, or winter plantings were made. There were significant differences between cultivars in the degree of PLRV resistance and susceptibility, independent of location, season, or year. Of the cultivars included in at least 2 trials each, the most resistant were Delcora, Omega, Spunta, and Whitu. Most susceptible were Cadima, Denali, Elliot, Renova, Russet Burbank, and Tor. Contrary to earlier reports, Spunta was resistant, while Delaware was relatively susceptible. Four Australian-bred cultivars (Cadima, Elliot, Geographe, and Tor) that were tested for the first time had little or no resistance, and 2 (Bremer and Toolangi Delight) were intermediate. The incomplete (quantitative) nature of resistance to initial infection with PLRV by viruliferous aphids was demonstrated in a seventh field trial where aphids were more abundant and all plants became infected, including resistant cultivars Delcora and Omega.