This investigation was undertaken to determine (a) whether the intravenous administration of neoarsphenamine and mapharsen affects the synthesis of cholic acid and, if so, (b) whether the oral administration of dehydrocholic acid for three days prior to and after the administration of the arsenicals will diminish the hepatotoxic action of these arsenicals. This study was stimulated by the clinical report that the administration of sodium dehydrocholate ameliorates arsenical hepatitis.1 In a previous study2 we attempted to ascertain the physiologic rationale of the claim, and found that sodium dehydrocholate did not increase the excretion of the arsenicals in the bile. In fact, sodium dehydrocholate tended to decrease and sodium glycocholate and sodium taurocholate tended to increase the excretion of arsenic in the bile. These tendencies were not statistically significant and could have been due to chance or random sampling. However, an increased excretion of