Thiamine and other vitamins of the B complex group are highly : ensitive to γ-radiation in aqueous solution owing to their high reactivity with the primary species formed by radiolysis of water, viz. hydrated electrons and hydroxyl radicals. In order to protect these compounds from radiolytic degradation, nitrous oxide and oxygen have been used as scavengers for the hydrated electrons and glucose for the hydroxyl radicals. By comparison of uv spectra it is shown that the above vitamins do not undergo radiolytic degradation in presence of nitrous oxide and glucose or oxygen and glucose. The importance of these results in connection with the sterilization of vitamin preparations is discussed.