The authors assessed the ability of a standard set of freshwater single species toxicity test to predict accurately effects of the insecticide diflubenzuron (1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea) on complex laboratory stream communities. The single-species tests complied with requirements prescribed for establishing freshwater quality criteria and included nine freshwater animal acute tests, five freshwater animal chronic tests, and one freshwater algal test. The stream communities were stocked from a natural source, equilibrated for 3 mo and then treated with diflubenzuron for 5 mo. Effects on these stream communities were assessed at the functional group level using biomass and diversity for the analysis.