RIMARY CARCINOMA of the liver holds a P unique position among all human neoplasms: First, because of striking differences in racial and geographical distribution, the problem, has world-wide significance. Second, it is so regularly associated with a chronic degenerative and regenerative disease (cirrhosis) of a large parenchymatous organ. Such association is rarely seen in other large organs such as the pancreas and kidney. Third, tumors occur spontaneously and can also be easily produced in experimental animals by different carcinogenic agents that damage the liver. Lastly, certain inherent difficulties are encountered in both the clinical and pathological aspects of the disease. The clinical problem is often one of diagnosing carcinoma in the presence of cirrhosis or distinguishing primary from secondary carcinoma of the liver. From the standpoint of pathology, there is such variation in histological structure that the determination of histogenesis and hence classification of some neoplasms of the liver have been almost impossible. Knowledge of cancer of the liver is today advancing in many areas-morphological, chemical, pathogenetic, etiological, and clinical. It is now possible to recognize most tumors as primary in the liver on the positive basis of their microscopic appearance rather than, as formerly, merely by exclusion of other possible sites. The chemical studies have gone far in characterizing the enzyme patterns and chemical composition of hepatoma as contrasted with normal liver tissue; unfortunately, no distinctive features are yet recognized that can supplement histopathological studies for precise diagnosis, although chemical determinations of certain changes in the host may be of aid in laboratory diagnosis during life. The