Varieties of United States tobaccos, tobacco introductions, and wild Nicotiana species were tested in the laboratory and in the field for resistance to the green peach aphid, Myzus persicae (Sulz.). Selections and crosses of resistant tobacco were less susceptible than any of the standard burley tobacco varieties. Ky. 61, TI 566B, and TI 567 were more susceptible than the other tobacco varieties tested. Nicotiana gossei, N. repanda, and N. trigonophylla were highly resistant, but crosses of N. gossei with N. tabacum did not show the high resistance of the N. gossei parent. The senescing leaves of the resistant wild species were much more susceptible to aphids than the young or mature leaves. The glucose content of N. gossei leaves was very low compared with that of leaves of susceptible plants, but from preliminary tests this relationship did not seem to be true for other resistant species.