Technical Abstract: Selenium exists in many different forms. How and where selenium is used and ultimately eliminated from the body largely depends on the form consumed. Furthermore, the reproductive state of an animal can alter the rate selenium is utilized. To further explore how organically bound forms of selenium are metabolized and how this metabolism is altered due to reproductive state, we fed lactating, pregnant and virgin rats either a selenocystine or selenomethionine diet providing 2 ug selenium/g diet/day for 18 days. Regardless of physiological state, feeding selenomethionine resulted in more selenium being stored in most tissues than when selenocystine was fed. This effect is likely due to the direct incorporation of selenomethionine into protein in place of methionine. More selenium was found in tissues of lactating compared to pregnant and virgin rats. This result is probably due to the increased food intake that is commonly associated with lactation.