During the past year, the activity of this group has increased dramatically. This is the result of several years spent building a technical base that is now coming to fruition. In general, the focus of this group is to describe how mammalian cells get rid of hydrogen peroxide and other oxygen radicals. Most of the work has concerned glutathione peroxidase. This enzyme is a selenium dependent enzyme which has been very well studied in animals but about which little is known in man. We became interested when experimental evidence showed that selenium effected the toxicity of adriamycin. Our interest was further stimulated by the growing evidence that selenium modulates the action of several carcinogens and may be an important anticarcinogen in man. This has been rendered more understandable by the recent evidence that oxygen radicals such as superoxide and hydroxyl radical as well as peroxide are critical in both carcinogenesis and promotion. With this background in mind, we have been following a broad based research plan to delineate the relevant biochemistry in man and animals.