Organisms selected for testing the toxicity of estuarine sediments must exhibit sensitivity to toxicants while remaining tolerant of wide ranges of salinities and sediment characteristics. The amphipod Leptocheirus plumulosus Shoemaker is an ecologically important infaunal inhabitant of Chesapeake Bay sediments. Leptocheirus plumulosus was exposed to a range of salinities and sediments varying in physical composition for up to 28 d in separate experiments to determine effects of natural environmental variables on amphipod survival and reproduction. No significant differences in adult survival were observed among salinity treatments ranging from 1.5 to 32 ppt or among sediment treatments varying in particle size and organic content. Significant effects on reproductive end points were detected, indicating the potential for incorporating sublethal end points into the bioassay. Acute 96-h LC50 values for aqueous cadmium at a salinity of 6 ppt were determined for Leptocheirus plumulosus and the amphipod Hyalella azteca Saussure, an organism commonly used in freshwater sediment toxicity tests. The LC50 values were 0.30 mg Cd per liter and 0.19 mg Cd per liter for Leptocheirus plumulosus and Hyalella azteca, respectively.