Studies were made on the effect of DDT (dichloro-diphenyl-trichloroethane) on the control of common potato insects in 3 potato growing areas of Minnesota. Large commercial potato fields were used with randomized and replicated plots ranging from 0.383 acre to 2.12 acres each, dusted with 1, 2.5 and 5% DDT dust in Pyrax ABB, applied by power field machinery in a regular dusting schedule during the growing season of 1943 in comparison with other insecticides and fungicides. Special attention was given to the control of potato fleabeetle, Epitrix cucu-meris; potato leafhopper, Empoasca fabae; aster leafhopper, Macrosteles divisus; tarnished plant bug, Lygus oblineatus; Colorado potato beetle, Leptinotarsa desem-lineata; alfalfa plant bug, Adelphocoris lineolatus; and the rapid plant bug, A. rapidus. The efficacy of the insecticides was detd. by periodic insect surveys[long dash]before each dusting, within 24 hrs. after each "dusting, and at other times before the next application. A record of ecological conditions during the applications and insect counts was kept. Statistical treatment of data gave highly significant results. The analysis of variance for treatment differences showed highly significant differences in fleabeetle and leafhopper populations as well as tarnished plant bugs for 2 weeks after each dusting. DDT proved to be an extremely valuable insecticide even in as low cones, as 1% against the mandibulate and haustellate insects. It gave strikingly good control of fleabeetles within 24 hrs., slightly less effective against leaf-hoppers, and the mortality of the tarnished plant bugs sornewhat increased at the end of the 6-day period after application. DDT also showed some fungicidal value against early and late blight of potatoes. Its residual properties may be a limiting factor in the general use of it. The question of its toxicity to higher animals is briefly discussed.