In a previous communication1 we have discussed in detail the rationale of the Quick hippuric acid test for hepatic function and have considered its reliability as an index of hepatic damage in cases of hepatic disease and of disease of the biliary tract. In this second communication we shall consider its value as an index of hepatic function in the presence of thyroid disease, for which purpose we have been employing it for the past eighteen months. Before discussing it from this aspect, however, it is necessary to consider the justification for any test of hepatic function under these circumstances, which means that we must trace the relation between the liver and the thyroid gland. It is surprising to find how commonly that relation is ignored. The majority of writers list hyperthyroidism as the chief cause of death of toxic thyroid disease, but they make no attempt to explain