Selenium (Se) metabolism in humans is discussed. More selenium as selenomethionine (Semet) is absorbed than when it is present as selenite (95-97% vs. 44-70%). The selenium content in blood is correlated with GPX activity in selenium-deficient Chinese and in New Zealanders, but it is not correlated in blood of subjects living in the states of Oregon or South Dakota in the United States. Selenium from Semet accumulates in blood at a faster rate than selenate, but there are no differences in the GPX activities. Similarly, no differences occurred in the accumulation of selenium in GPX when Semet was compared to selenate, but a difference was found in the accumulation of selenium in hemoglobin (erythrocytes) and albumin (plasma) in subjects taking these two forms of selenium. The majority of selenium in plasma is usually present in selenoprotein P, but with high intakes of Semet, the amount in albumin predominates. Stable isotopes were used to develop the concept of ''selenite exchangeable pool,'' which can be employed to assess the body burden of selenium in humans. The renal clearance of selenium is higher for Semet than selenate. Even though the maximum safe intake of selenium for humans was estimated to be 600 g per day, with use of a safety factor, 400 g was suggested as the maximum safe intake on a long-term basis. An intake of 40 g was suggested as the minimum amount required for humans, and intakes of less than 11 g will definitely put people at risk of deficiency. J.