INJECTION of beef or hog thyroglobulin into experimental animals causes an increase in basal metabolic rate and antagonizes the action of antithyroid drugs. These effects are similar to those following the injection of thyroxine. There is yet no adequate explanation for the fact, reported by various workers1, that these thyroglobulins are more effective than can be accounted for by the liberation in the body of the thyroxine they contain. More recent observations have demonstrated the varying ability of different species to remove homologous and heterologous thyroglobulins labelled with iodine-131 from the circulation2. An attempt is now being made to correlate the metabolism of different thyroglobulins with effect on the basal metabolic rate at the same dose-level. This communication concerns the absorption, metabolism and metabolic effects in the rabbit of purified dog thyroglobulin.