Five American Cyanamid Company experimental organophosphorus systemic insecticides, compounds 43064, 43356, 47031, 47071, and 47470, have been evaluated in the laboratory and greenhouse to determine their usefulness for systemic control of cotton-insect pests. Topical treatments of adult boll weevils, Anthonomus grandis Boheman, with the 5 experimental insecticides indicated that they were more toxic than phorate, but resulted in unusually flat dosage-mortality curves. Seed treatments of cotton with compounds 43064, 43356, and 47071 gave excellent control of adult boll weevils in greenhouse experiments for 10 to 11 weeks. Treatments with the phorate standard controlled weevils for only 6 weeks. Field experiments, however, indicated that compound 43064 was no more effective than phorate for control of aphids, thrips, or boll weevils, Chemical names of American Cyanamid Company compounds tested are: 43064, cyclic ethylene (diethoxyphosphinothioyl) dithioimidocarbonate; 43356, cyclic ethylene (dimethoxyphosphinothioyl) dithioimidocarbonate; 47031, cyclic ethylene (diethoxyphosphinyl) dithioimidocarbonate; 47071, cyclic propylene (diethoxyphosphinothioyl) dithioimidocarbonate; 47470, cyclic propylene (diethoxyphosphinyl) dithioimidoearbonate.