Ascorbate (ascorbic acid, vitamin C) is one of the early, unorthodox treatments for cancer. The evidence upon which people base the use of ascorbate in cancer treatment falls into two categories: clinical data on dose concentration relationships, and laboratory data describing potential cell toxicity with high concentrations of ascorbate in vitro. Clinical data show that when ascorbate is given orally, fasting plasma concentrations are tightly controlled by decreased absorption, increased urine excretion, and reduced ascorbate bioavailability. In contrast, when ascorbate is administered intravenously, concentrations in the millimolar level are achieved. Thus, it is clear that intravenous administration of ascorbate can yield very high plasma levels, while oral treatment does not.