Selenium is a possible cancer preventive agent, and is being considered for use in intervention trials. A study in collaboration with the Cancer Prevention Studies Branch is in progress which will provide information on the pharmacokinetics of selenium in its prototype forms -- sodium selenite (inorganic form) and selenomethionine (organic form). This information is unavailable for these agents in the dose currently considered optimal, and is necessary to the determination of time and manner of administration. Parameters such as percent absorption, maximum concentration, time to maximum concentration and mean residence times will be estimated for a single dose and compared in fasting and non-fasting subjects. In order to interpret the study data more fully, development of integrated kinetic models, one for selenite and one for selenomethionine, is underway. Such models are useful in making inferences about drug metabolism and about the distribution of the drug in various body pools. A model for selenite has been developed based on pilot study data and is being tested on data from the main study. It is anticipated that the models will allow estimation of mean residence times and rates of exchange between body pools. Another aspect of the project is an analysis of variations in total selenium levels in the plasma, urine and feces both within and between individuals. This information is important in deciding what measures can be used to determine selenium status. The Biometry Branch, in cooperation with the Cancer Prevention Studies Branch, is functioning as a data collection center, had primary responsibility for the study design, and has primary responsibility for data analysis.