An in vivo metabolism study in humans was carried out to investigate the toxicokinetics and metabolism of sodium selenate differentiating by the trimethyl-selenium (TMSe) status. Therefore, the changes in blood plasma concentration and the urinary excretion within 24 h of seven healthy subjects after oral administration of a dietary supplement containing sodium selenate (50 mu g selenium) were analyzed. Three subjects belong to the subgroup of TMSe eliminators, and four subjects were related to the non-TMSe eliminators subgroup. The concentrations of total selenium in blood plasma and urine samples were determined by inductively coupled plasma-mass spectrometry (ICP-MS). Additionally, speciation analysis of urine samples was performed using ICP-MS coupled to a liquid chromatography system. Plasma selenium concentration changed from 82.5 +/- 12.5 mu g Se/L before to 85.1 +/- 12.0 mu g Se/L 2-3 h after supplementation. Considering the individual 24-hour background amounts of renal excreted selenium, the ingestion caused an additional excretion of 15.4 +/- 3.3 mu g Se/24 h ((=) over cap 31.1 +/- 7.6 % of the administered dose) with a maximum elimination already 2 h after exposure. The differentiated analysis revealed that in all subjects, the main elimination product (30.1 +/- 6.9 % of the administered dose) was unmetabolized selenate. TMSe was only detected in the urine of the TMSe eliminators. This subgroup excreted in comparison with the non-TMSe eliminators a significantly lower amount of selenate. Only one subject metabolized selenate to a larger portion to methyl-2-acetamido-2-deoxy-1-seleno-beta-D-galactopyranoside (SeSug1) and methyl-2-amino-2deoxy-1-seleno-beta-D-galactopyranoside (SeSug3). All other subjects showed only a minor metabolism of selenate to selenium-containing carbohydrates. By individuals, which do not excrete TMSe in urine basically, selenate is metabolized only marginally and is excreted rapidly via urine generally. In contrast, a considerable portion of this inorganic selenium compound is metabolized by individuals, which eliminate TMSe basically. An elevated metabolism may also be provided by individuals, which eliminate high levels of selenium-containing carbohydrates basically. The difference in metabolism may imply a different disposition for pharmacological or toxic effects by exposure to inorganic selenium compounds.