Ducks were collected from a marine environment known to be polluted with heavy metals. Gel elution profiles were determined for both liver and kidney tissue using Sephadex G-75 gel. Zn increased linearly on the high molecular weight protein pool until this pool was apparently Zn saturated; saturation levels were 0.06 mumole cytoplasmic Zn/g kidney (wet wt.) and 0.14 mumole cytoplasmic Zn/g liver (wet wt.). Seventy-five percent of cytoplasmic Cd was found on the high molecular weight protein pool unless it was Zn saturated. If this pool was Zn saturated, then excesses of Zn and up to 75% of cytoplasmic Cd appeared on metallothionein. Results are discussed in terms of a competition of Cd and Zn for Zn binding sites on metalloenzymes. Cu increased linearly on both the high molecular weight protein pool and metallothionein, with increases of Cu in tissue.