The foregoing report on aphid resistance in potatoes considers the problem in the following manner: 1. Reference is made to previous studies on insect resistance in plants which have some bearing on aphid resistance in theSolanum genus. 2. The procedure and results of experiments carried on over the period of 1939–'45 to test aphid reactions critically in approximately 20 varieties ofSolanum tuberosum and 5 otherSolanum species, and generally in 90 other varieties, are described. The test aphids in all cases were of the speciesMyzus persicae Sulzer. Reactions have been classed as “very susceptible” (typically S. #41,956, Katahdin), “susceptible” (typically Bliss Triumph, Irish Cobbler, Sebago, Pontiac, Chippewa), “tolerant” (typically Green Mountain, President, Warba, Arran Vic-Solanum chacoense), and “very resistant” (Fredericton Sdlg. #996-1-4 Houma, Earlaine, Sequoia,Solanum demissum, Solanum Commersonii, Solanum chacoense), and “very resistant” (Fredericton Sdlg. #996-1-4 andSolanum polyadenium). 3. A discussion notes that potato varieties and species differ materially in their reactions to the feeding of aphid populations. Consideration is given to the possibilities of breeding potatoes resistant to aphid populations, both for the entomological and pathological value. A similarity between results obtained in leafhopper resistance studies and those found in aphid studies is noted. 4. Tables, graphs and figures are utilized wherever possible for clarity.