Technical Abstract: Cotton (Gossyium hirsutum L.) desiccants and defoliants are not consistenly efficacious. We are systematically determining causes for inconsistency of several compounds. Low absorption (or uptake) of compound into the leaf could limit efficacy. The effects of adjuvants upon uptake of radiolabeled compound applied to individual leaves was examined. Ammonium sulfate increased uptake of fluthiacet-methyl and endothall during evening treatments, but decreased paraquat uptake during some conditions possibly due to paraquat salt formation. Pelargtonic acid had less influence on uptake, and relatively more influence on efficacy of paraquat and endothall. Pelargonic acid and Eth-N-Gard most consistenly maximized uptake of fluthiacet-methyl during morning and evening. If consistency of efficacy can be enhanced, then the tempation to apply these herbicidal compounds in excess will be lessened, and environmental quality preserved.