Microcosm experiments were conducted to evaluate the relative toxicity of sediments taken from dredge sites in the Port of Hampton Roads, VA. The multiple species microcosm were designed to allow natural assemblages of zooplankton and benthos to be exposed to dredged materials under more realistic conditions than achieved in bioassays. Changes in community structure and body burdens of contaminants were monitored in the microcosms following “dumps” of the sediments. The biological effects of exposure to dredged materials under the microcosm conditions were subtle. Zooplankton community structure was only affected by treatments involving sediments known to be most contaminated with polynuclear aromatic hydrocarbons and metals. Likewise, statistically significant changes were observed in the composition of benthic communities exposed to the most contaminated sediments. Motile forms appeared to have migrated from the contaminated sediments in various degrees while more sedentary species displayed mortalities relative to the controls. Body burden studies indicated that experimental animals did not accumulate significant concentrations of metals or chlorinated hydrocarbons in any of the treatments. However, biota exposed to the contaminated sediments did accumulate certain of the polynuclear aromatic hydrocarbons known to be major pollutants in the port.