1. Quantitative selenium metabolism has been studied in normal young New Zealand women by measuring total Se intake and urinary and faecal Se output, and by using values for absorption, excretion and turnover of 75Se determined after administration of [75Se]selenomethionine or [75Se]selenite.
2. In a period of 14 d when a normal ad lib. diet was being consumed, mean dietary Se for four women was 24.2 μg/d, mean urinary Se was 13.1 μg/d and mean faecal Se was 10.8 μg/d; mean Se balance during this time was +0.3 μg/d.
3. Intestinal absorption of food Se was 0.76−0.83 of intake (mean 0.79).
4. Whole-body Se was calculated in three different ways; (a) using the specific activity of urinary Se and retained whole-body 75Se; (b) using plasma Se and the occupancy of 75Se in whole-body and plasma; (c) using absorbed food Se and the occupancy of absorbed 75Se in whole-body.
5. Whole-body Se calculated from measurements obtained following the administration of [75Se]seleno-methionine was 4.7−10.0 mg (mean 6.9) using method (a), 4.1−7.2 mg (mean 5.2) using method (b) and 4.3−8.9 mg (mean 6.2) using method (c).
6. Whole-body Se calculated from results obtained after giving [75Se]selenite was 2.7−3.4 mg (mean 2.9) using method (a), 2.3−5.0 mg (mean 3.5) using method (b) and 2.1−3.0 mg (mean 2.6) using method (c).
7. The results of this study indicate that the minimum dietary requirement of Se for the maintenance of normal human health is probably not more than 20 μg/d.