Standardized toxicity testing protocols for assessing chemical hazards to aquatic organisms inadequately consider behavioral effects of toxicants; yet, organisms behaving abnormally in the wild experience reduced growth, fitness, and higher mortality. This study determined the effects of cadmium (0, 30, 60, 120, and 240 [mu]g/L) on juvenile bluegill (Lepomis macrochirus) foraging behavior in three 28-d functional response experiments, and one 24-d multi-prey experiment. The study also examined how cadmium-altered behaviors contributed to reduced growth rates. Different sizes of Daphnia magna and D. pulex were used as prey in these experiments. The rate of change (i.e., trends over time) in the number of Daphnia attacked per unit time was the most consistently sensitive behavioral measure of sublethal stress in exposed bluegill; the lowest observed effect concentration (LOEC) for this metric was 30 [mu]g Cd/L. The magnitude and duration of effects on prey attack rates were inversely related to prey size; cadmium had a greater and more prolonged effect on fish foraging on small compared to large prey. Cadmium had little effect on prey capture efficiency and handling time. Patch switching efficiency, as measured by caloric gain per unit time, was not affected by cadmium exposure. Cadmium affected prey selection when preferred prey were scarce, but not when preferred prey were abundant. Evidence suggests that reduced consumption of Daphnia and altered prey selection were the result of cadmium-altered prey search strategy and perhaps reduced motivation to feed. Growth was significantly reduced in bluegill exposed to nominal concentrations of 30 [mu]g Cd/L in two of three experiments and at 60 [mu]g Cd/L in the third experiment;In managing environmental contaminants, exposure must be limited to concentrations that protect organisms' ability to carry-out their most basic and essential ecological activities (i.e., feeding, surviving, and reproducing). Behavioral toxicity tests provide a powerful tool for achieving this goal. By understanding toxicant effects on fish foraging behavior, toxicologists can also begin to utilize optimal foraging and bioenergetics models to predict toxicant-altered diets and growth in the field.