The composition of neutral and amino sugars in different preparations of hog thyroglobulin and in thyroglobulins obtained from various animal species, i.e., amphibia (Xenopus laevis), aves (chicken), and mammals (whale, monkey, and human) was determined. In determining neutral sugar compositions, gas-liquid chromatography of the alditol acetates was performed, while amino sugars were analyzed by ion-exchange chromatography. 1. All the thyroglobulins studied were glycoproteins containing both neutral and amino sugars. Fucose, mannose, galactose, and glucosamine were common constituent sugars, and a small amount of galactosamine was found in thyroglobulins other than hog and Xenopus laevis. 2. Different subtractions of hog thyroglobulin obtained by DEAE-cellulose chromatography and a preparation of noniodinated thyroglobulin prepared from goitrogen-treated hog showed essentially the same composition of neutral and amino sugars, irrespective of the large differences in iodine content. A slightly different composition was observed with one minor subtraction only, in which the mannose and glucosamine contents were somewhat lower than those of other subtractions, and noniodinated hog thyroglobulin contained a slightly lower amount of glucosamine than normally iodinated hog thyroglobulin. 3. Considerable differences in the composition of neutral and amino sugars were found among amphibian, avian, and mammalian thyroglobulins. Xenopus laevis thyroglobulin was richest in carbohydrate content, whereas chicken thyroglobulin, having a moderate sugar content, revealed a somewhat different neutral sugar composition from that of other thyroglobulins. Even among mammalian thyroglobulins, distinct species specificity was found in most cases. Whale thyroglobulin, in particular, had the lowest neutral and amino sugar content of the thyroglobulins studied. No significant difference was observed between the carbohydrate compositions of human and monkey thyroglobulins.