A test method was developed to assess the toxicity of freshwater dredged sediments. Toxicity of contaminated sediments was detected by monitoring survival and growth of fathead minnows (Pimephales promelas), emergence and egg hatchability of midges (Paratanytarsus parthenogenica), survival and reproduction of daphnids (Daphnia magna), and changes in microorganism populations. All organisms were exposed for 21 days in an apparatus that recirculated water through a compartment containing the sediments. In addition, a ranking scheme was proposed with which bulk sediment analyses for chemical contaminants could be condensed into a single value termed the hazard index. The hazard index was calculated for each sediment sample and was indicative of the degree of chemical contamination of the sediment. Sediments were classified as highly polluted, moderately polluted, or relatively nonpolluted, based on their hazard index. Eighty-six dredged sediment samples were tested. All biological parameters measured, except midge egg hatchability, were instrumental in detecting toxicity associated with the sediments. Effects were observed with 74% of the highly polluted sediments, 38% of the moderately polluted sediments, and 36% of the relatively nonpolluted sediments. The sublethal parameters measured were important indicators of toxicity.