This research compares effects of heavy metals on macroinvertebrate communities in outdoor experimental streams with those observed at impacted field sites. Natural assemblages of aquatic macroinvertebrates were established on substrate-filled trays which were then transferred to outdoor stream mesocosms. Exposure of these communities to low levels of copper and zinc (target concentration = 12 μg/L) significantly reduced the number of taxa, number of individuals, and abundance of most dominant taxa within 4 d. After 10 d, control streams were dominated by Ephemeroptera and Tanytarsini chironomids, whereas treated streams were dominated by Hydropsychidae and Orthocladiini. Responses of benthic communities to metals observed at the Clinch River (Russell Co., Virginia), a system impacted by copper and zinc, were similar to those in experimental streams. Ephemeroptera and Tanytarsini, which comprised 38–46% of the macroinvertebrate community at upstream reference stations, were significantly reduced at all effluent sites. As in treated experimental streams, impacted stations were dominated by Hydropsychidae and Orthocladiini. The similarity of our experimental results to those obtained from Clinch River field sites suggests that outdoor stream mesocosms may be employed to predict macroinvertebrate community responses to heavy metals.