Intravenous vitamin C increases blood levels that are 100-500 times higher than levels that can be achieved with oral ingestion. It is this VERY-high concentration of vitamin C in the blood that generates hydrogen peroxide that selectively kills cancer cells. Early phase 1 clinical trials showed that the combination of high-dose, intravenous vitamin C with standard chemotherapy or radiation was well tolerated and improved patient outcome. Larger clinical trials are now underway.