Formulations of Elcar (B. heliothis) consisting of potential adjuvants were evaluated in standardized laboratory bioassay tests against 24-h-old Heliothis zea (Boddie) larvae. A cottonseed flour adjuvant consisting of 62.5% cottonseed flour, 12.5% cottonseed oil, 25% sucose and 0.004% Tween 80 caused significantly higher bioassay mortality rates than the other adjuvants evaluated or than a standard Elcar-water formulation. Evaluation of the individual constituents of this adjuvant indicated that the cottonseed flour or those combinations including cottonseed flour caused significantly higher mortality rates than did either the individual or combinations of cottonseed oil, sucrose, or Tween 80. The compatibility and potential of selected gustatory, thixotrophic, protective, and surfactant agents indicated that these agents may cause slight inhibition of the insecticidal activity of the formulations. The amount of cottonseed flour in the test formulations was directly related to insecticidal activity; activity decreased as flour content was reduced from 15% (highest) to 0.5% (lowest). Formulations containing 7.5% cottonseed or soybean flour provided the most consistent mortality rates and represented the upper limit of mixability. No differences in mortality rates occurred among a 7.5% cottonseed flour, a 7.5% cottonseed flour hydrolyzate, and a 5% cottonseed flour formulation, indicating that the active factor(s) is water soluble and is not related to particulate size or content. The addition of various adjuvants to formulations containing Elcar increased bollworm bioassay mortality rates 8- to 10-fold in laboratory tests.