We have demonstrated that snakes and some other reptiles normally possess high plasma zinc concentrations. These levels are similar to those measured in teleost fish. Plasma zinc levels in the range of snakes and teleosts have been shown to be toxic to crocodilians and mammals. Zinc has been shown to bind to a specific protein in albacore and winter flounder serum. Previous experiments suggested a similar protein in snake plasma. Western blot techniques were used to search for proteins capable of binding large quantities of zinc with high affinity in the plasma of a wide range of vertebrate species. These data were compared to plasma zinc concentrations measured by atomic absorption spectrophotometry. A correlation between high zinc levels and the presence of specific zinc-binding proteins different from mammalian albumin was observed. Snakes and teleost fish demonstrated both very high plasma zinc concentrations and a zinc-binding protein. Teleosts and snakes have significantly higher levels of plasma zinc than birds and mammals.