ONE OF the major objectives in the study of the biochemistry of cancer is to establish a difference in the nature or quantity of enzymes present in normal and in malignant tissues. If it could be shown that a malignant tumor contained an enzyme not present in a benign tumor of the same type or in normal tissue of the cell type from which the tumor was derived, then it might be possible to inhibit selectively the enzyme peculiar to the tumor and consequently impair the growth of the tumor without affecting the metabolism of the normal cells. Furthermore, if it could be demonstrated that the activity of an enzyme in normal cells differed from that in malignant cells, the pathogenesis of the change from a benign to a malignant state might become apparent. In the past few years investigation of the enzyme systems of normal and malignant melanogenocytes 1