Adult Elasmopus rapax, collected from the eastern coast of Venezuela in 1990, were exposed to seawater containing various CdCl2 concentrations ranging from 0.25 to 5.5 μmol l-1. The 48-h and 96-h LC50 values obtained were 4.0 and 1.6 μmol Cd l-1, respectively. In amphipods exposed to 1 μmol Cd l-1 for up to 240 h, the apparent rate of cadmium uptake was higher in dead animals (most of which had molted during the preceding 24 to 48 h) than in those which survived throughout the treatments without molting. Thus, whole-body cadmium content reached 1.74 μmol g-1 dry weight (dw) in the former and only 0.85 μmol g-1 dw in the latter; the higher body Cd-load may have caused the increased mortality observed in molters. On exposure to cadmium levels above 0.5 μmol l-1 the oxygen consumption rate of non-molters decreased from 2.2 to about 1.5 ml O2 g-1 dw h-1 over the first 24 h, remaining unchanged thereafter. The results place E. rapax among the most sensitive marine organisms yet studied concerning cadmium toxicity, and emphasize the usefulness of the Amphipoda as bioindicators and research tools for bioassays.