The influence of various salts, chelates, and other complexes of zinc given by gavage on serum zinc levels in rats was studied. Serum zinc concentrations were determined over 6 hr after administration of zinc sulfate at doses of 5, 10, 20, 50, and 100 mg of zinc/kg. Serum zinc levels following doses of zinc salts and complexes were compared with those after zinc sulfate. Phytic acid, aminopolycarboxylic acids (including edetate disodium), and penicillamine significantly suppressed increases in serum zinc concentration. Some natural amino acid-zinc sulfate mixtures (those with lysine, cysteine, glycine, and histidine) produced greater levels than the equivalent dose of zinc sulfate alone. Several thiocarboxylic acids, such as mercaptoacetic acid and thiosalicylic acid, also increased serum zinc concentrations. These observations form a basis for attempted modification of zinc absorption in other species.