One phase of an evaluation of antimycin as a piscicide in ten ponds and lakes in the Southeast involved a study of its effect on plankton and bottom organisms. Net zooplankton in the groups Cladocera, Copepoda, Rototaria and nauplii larvae were enumerated before and after the application of 5.0 ppb antimycin. All groups were severely reduced and some disappeared following the treatment. Bottom organisms in the groups Tendipedidae, Ceratopogonidae and Culicidae were enumerated. Bottom organisms in these groups did not disappear following antimycin applications. Probably reasons are discussed.