Potato virus Y (PVY) is a reemerging problem in potato production in North America. Although the "ordinary" strain, PVY o, is still the dominant isolate in U.S. seed potatoes, the recombinant strain of the virus PVY N-Wi (= PVY N:O) has become widespread. An increase in the prevalence of a PVY strain could be due to differences in the efficiency of transmission by aphid vectors. The transmission efficiency by a clone of Myzus persicae was determined for five isolates each of PVY o and PVY N-Wi. An aphid transmission assay was developed based on the use of potato seedlings from true potato seed, allowing for greater control of plant age and growth stage. No apparent differences in transmission by M. persicae were observed. Single isolates of PVY o and PVY N-Wi were tested for their ability to be transmitted from potato to potato by five aphid species: Aphis glycines, A. gossypii, A. nasturtii, M. persicae, and Rhopalosiphum padi. Both PVY isolates showed a similar transmission phenotype in being transmitted efficiently by M. persicae but very poorly or not at all by A. glycines, A. gossypii, and R. padi. The aphid A. nasturtii transmitted both isolates with an intermediate level of efficiency. The data do not support a model for a differential aphid transmissibility being responsible for the increase in the prevalence of PVY N-Wi.