Response surfaces describing the response of yield of cotton to the simultaneous injury of bollworm, Helicoverpa zea (Boddie), tobacco budworm, Heliothis virescens (F.) and infestation of cotton fleahopper, Pseudatomoscelis serialus (Reuter) were developed. These surfaces were developed for Stoneville 13, TAMCOT CAMD E, TAMCOT SP 37, and TAMCOT SP 37H at one-third grown flower bud and Stoneville 13 at sixth true-leaf stage of growth in Corpus Christi, Texas. Injury and infestation of these insects were combined additively. Multiple pest economic injury levels were developed from these response surfaces and recent economic considerations. Response surfaces varied greatly with cultivars. Stoneville 13 was the most tolerant and TAMCOT SP 37 was the most susceptible to the combined effects of both insects. Economic injury levels for one insect change and must be calculated separately for each level of injury or infestation of the other insect.