The incidence and mortality rates from most cancers increase exponentially with age. It is likely that this aging phenomenon is partially due to specific changes that occur in the host resulting in an increased susceptibility to neoplasia. Our hypothesis is that one such host factor is a deficiency in GSH, based on the importance of this compound in the detoxification of a wide variety of exogenous and endogenous carcinogens and free radicals, as well as in the maintenance of immune function.