Abstract An inter-laboratory comparison of the Swartz et al. (1985) amphipod sediment toxicity test was performed for seven marine sediments of and one a posteriori hypotheses or criteria were tested for three end points (survival, emergence and reburial). The bioassay met the a priori criterion of success, acceptable survival and behavior (emergence and reburial) of controls. It also met two of three a priori hypotheses: acceptable agreement on the rank order of toxicity for all three end points and acceptable agreement on mean values for the end points. The third hypothesis, classification of sediments as toxic or non-toxic, was only met for the emergence end point; however, this was probably due to the narrow range of toxic sediments tested (four of the seven sediments tested were only marginally toxic). Review of these and other amphipod sediment toxicity test data indicates that sediments that are clearly nontoxic (survival is greater than 87%) and those that are clearly toxic (survival is less than 76%) will be accurately classified whereas those of marginal toxicity (survival is between 76% and 87%) can only be classified based on emergence data. An a posteriori comparison indicated that the amphipod sediment toxicity test was more precise in LC 50 and EC 50 determinations with a reference toxicant (cadmium-amended sediments) than has previously been shown in inter-laboratory comparisons. Based on the results of this study, we recommend the wider use of this toxicity test to determine the toxicity of field-collected marine sediments and for laboratory studies with contaminant-amended sediments.