ABSTRACT The coincidence between iodine-concentrating ability and peroxidase activity in salivary glands has been studied. In 19 of 24 types of salivary glands examined the two activities either occurred together or were both absent. 3 of the glands gave inconclusive data. The iodine metabolism was studied in the three main salivary glands of six different animal species. Paper chromatography of salivary gland homogenates revealed that 131I- injected intraperitoneally before salivary gland extirpation is only metabolized as iodide, whether or not the gland is capable of concentrating iodide or contains a peroxidase. The findings are discussed with special reference to some possible functions for peroxidase in salivary gland metabolism. The activities were not correlated either to the serous or to the mucous type of gland.