The role of vitamin B6 in the growth of Morris hepatomas and the development of enzymatic activity in the normal or hormonally induced state has not been investigated. In attempting to learn of malignancy, the proposal examines the relationship of the absence and presence of the vitamin to tumor growth and tumor metabolic function (enzyme activity). The effect of the absence of vitamin B6 from the diet on the growth of several hepatocellular tumor lines and the activity of tumor, host and normal liver tyrosine transaminase and its response to the administration of hydrocortisone will be studied. Enzyme activity is measured both chemically (i.e. product formation) and immunochemically. Tumor growth and enzyme activity will be determined in the normal and vitamin B6 deficient state and during progressive stages of deficiency under ad libitum and pair-feeding conditions. The response of transaminase activity to steroid administration in the presence and absence of protein synthetic inhibitors will also be studied in tumor- bearing and control animals and in both normal and deficiency states. If the absence of the vitamin results in regression of tumor growth limiting the availability of the dietary factor may prove to be an effective means of exercising a type of control over tumor growth.