The potential use of bioaccumulation by Daphnia magna as an analytical tool in studying properties of various aqueous cadmium forms is described. Selected aquatic chemical factors affecting cadmium residues were determined for organisms exposed to cadmium in the absence and presence of various organic and inorganic chemicals, some capable of strongly complexing cadmium. Without any added complexing agents, steady-state relationships were observed between total aqueous cadmium concentrations and bioaccumulated cadmium within 2-4 days of exposure. Residues were a nonlinear function of the concentration. The presence of humic acid, pyrophosphate, or aminopolycarboxylic acids, at sufficient concentrations to maximize complexation, was effective--to various degrees--in reducing cadmium uptake. However, cadmium in the presence of diethyldithiocarbamate bioaccumulated to a greater degree than in its absence.