Potato virus Y (PVY) has a very wide host range and the necrotic strain (PVY^N) has become the predominant strain on tobacco in Europe since 1953. This strain, however, is not homogenous and, during the last few years, new subgroups that break the known sources of resistance have been identified on tobacco and potatoes. It was therefore essential to re-examine the main sources of PVY resistance. Twenty PVY isolates from tobacco and potatoes were each artificially inoculated onto three varieties (VAM, Wislica, PBD6) and the wild species N. africana. Virgin A Mutant (VAM), carrying the mutated single recessive "va" gene, was not infected by Y^N from tobacco or by the three potato strains Y⁰ (ordinary strain), YWi (Polish), and Y Esp (Spanish). None of these isolates are detectable by monoclonal antibodies against typical necrotic strains. Similarly, this variety did not show symptoms after inoculation with some isolates of the NTN group either, including YDitta (Austrian) and YMu (Hungarian), and these strains are detectable by both antibodies produced by Bioreba. The VAM variety did become infected by the Polish isolates: Y^NZ, Y^NTN Gr and the Hungarian isolates: Y^NTNWa, Y^NTN Ha, all from tobacco, and by six Polish isolates, one Hungarian and two French, all from potatoes. Most of these isolates belong to NTN group and are detectable by both antibodies produced by Bioreba. The symptoms on VAM caused by these isolates varied, depending on the isolate; but were mainly necrotic and chlorotic rings, rather than veinal necrosis. All of the isolates that broke the "va" type of resistance also caused symptoms on the Polish variety Wislica, that carries a source of the PVY resistance from the oriental tobacco. However, there were some differences in the frequency of infected plants and the symptom expression. PBD6, a line obtained from Institut du Tabac de Bergerac, carries the PVY resistance from a Paraguayan origin, and therefore is not related to the resistance found in other varieties. This resistance was also broken by some of the Polish and Hungarian isolates from tobacco in this experiment. None of the twenty PVY isolates used in this experiment infected N. africana which shows that this species could be the best source of resistance.