Field and greenhouse readings in Maine together with test plot readings in Florida showed the incidence of potato leafroll virus infection in 10 Kennebec seed lots from south, central and northern Aroostook County to be about 1.2%. When the seed lots were indexed by aphid transmission of the virus toPhysalis floridana Rydb. in January and July the incidence of leafroll was found to be 2% and 10% respectively. SinceP. floridana detects mild strains as well as those capable of causing visible symptoms on potato, these results indicate that mild strains are present in the Kennebec variety being grown for seed in Aroostook County. The authors indicate, however, that leafroll symptom expression inP. floridana, in many instances, was not definitive and they suggest that their data may reflect an inaccurate estimate of the prevalence of mild strains of leafroll in Maine.