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Acute static bioassays were conducted with 13 pesticides to determine their comparative toxicity to fish. There was a wide range in the toxicity of these compounds with 96-hour TLm values ranging from 0.0033 to 4.0 mg/1. Of the compounds tested, Thiodan, a chlorinated hydrocarbon, and Thimet, an organic phosphorus pesticide, were the most toxic; and Bayer 29493, an organic phosphorus compound, and Fermate, a carbamate, were the least toxic. In about half of these static tests, toxicity increased significantly with an increase of exposure time from 24 to 96 hours. The toxicity of the organic phosphorus and chlorinated hydrocarbon compounds did not appear to be influenced by the water quality characteristics (pH, hardness, alkalinity) examined. The toxicity of two of the carbamates was influenced by water quality characteristics.