Among the most striking effects in medicine are glycemic modulation of tumor tolerance and the associated improvements in health of cancer patients that can occur within months in the well nourished but semi-fasting state. We cite evidence that strongly supports the old view' that neoplastic initiations are always occurring but, in the cancer-free population, are found and reversed by immune surveillance performed by leukocytes, as part of cell mediated immunity (CMI). Part of that evidence shows the 30, 100 and 10,000 fold increases in cancer incidence that result when immune surveillance is diminished by hyperglycemia or lost (as by thymectomy, etc). In essence, although not as drastic as thymectomy, hyperglycemia suppresses and hypoglycemia enhances immune surveillance (in the conditioned patient whose hypothalamic-pitukary-adrenal axis does not produce a lympholytic state by excessive elevation of cortisol). Our use of leukocytes includes three major nucleatea cells of the blood: granulocytes (or neutrophils), lymphocytes, and monocytes. The last two are effectors of CMI.