The concentration of zinc in oysters was highly variable — samples from relatively unpolluted estuaries of North Carolina contained, on the average, 85–245 ppm zinc, based on wet weight. Internal tissues, like adductor muscle and pericardial sac, had zinc levels less than half those of external tissues but zinc was nonetheless distributed uniformly throughout the animal tissues. During 1964–66, North Carolina oysters contained 2–20 pCi65Zn from fallout per 100 g wet weight. Specific activity of65Zn in these oysters during 1965–66 was in the range 90–300 pCi/g Zn, and was declining with an apparent half-life of 276 days.