An inter-laboratory comparison of the Swartz et al. (1985) amphipod sediment toxicity test was performed for seven marine sediments of varying toxicity. Five laboratories participated. Four a priori 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 agreemeent on the rank order of toxicity for all three 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. (Copyright (c) Elsevier Applied Science Publishers Ltd, England, 1986.)