The specific goal of this research was to conduct 24-hour static acute bioassays with 'untreated' influent and 'treated' effluent using fathead minnows (Pimephales promelas) and water flea (Daphnia magna) to biologically evaluate the effectiveness of industrial wastewater facilities in reducing effluent toxicity to aquatic organisms. Of primary interest to the EPA was an evaluation of the capacity of the wastewater treatment facilities of the pesticide industry for reducing toxicity. To accomplish the stated goal, on-site 24-hour static acute toxicity tests were performed during ten consecutive workdays at seven industrial sites. Five of the test sites are defined as pesticide manufacturers, while the remaining sites consisted of an organo-chemical manufacturer and a bleached-kraft paper mill. The effectiveness of the treatment plants was determined by performing static acute toxicity tests with the fathead minnow (Pimephales promelas) and the water flea (Daphnia magna) on samples of the wastewater collected before and after treatment. Results of the studies are expressed in terms of both median lethal concentrations (LC50's) as % effluent and lethal units. The data from these studies indicate that the wastewater treatment plants provided an average efficiency of 98% in reducing the toxicity of 'untreated' wastewaters. Neither species tested proved to be a more sensitive indicator of toxicity, though a larger data base is required to make valid appraisal. Of interest was the observation that while some wastewater treatment facilities provide good efficiency (98+%) in reducing toxicity, the resulting effluent still represented a relatively high number of lethal units. This was a result of the fact that the 'untreated' influent entering the waste treatment system contained a very high level of lethal units and a subsequent 98% reduction of that level still resulted in a toxic wastewater.