A human in vivo metabolism study was carried out to investigate the impact of the trimethylselenium ion (TMSe) status on metabolism and toxicokinetics of sodium selenite and selenized yeast. Nine healthy human volunteers were orally exposed to 200 A mu g selenium as sodium selenite and seven with selenized yeast (100 A mu g selenium). In each intervention group, three subjects belong to TMSe eliminators. Blood samples were withdrawn before and up to 6 h after administration. Urine samples were collected before and within 24 h after administration. Total selenium (Se) was quantified in blood plasma and urine and low molecular Se species in urine. Selenium concentration in plasma increased from 84.5 +/- A 13.2 A mu g Se/L before to 97.4 +/- A 13.2 A mu g Se/L 2-3 h after selenite supplementation and 89.5 +/- A 12.9 A mu g Se/L to 92.1 +/- A 13.9 A mu g Se/L after selenized yeast intake. The oral ingestion caused an additional Se elimination via urine of 16.9 +/- A 10.6 A mu g/24 h (TMSe elim.: 10.8 +/- A 6.9 A mu g/24 h; non-TMSe elim.: 20.0 +/- A 11.3 A mu g Se/24 h) after selenite exposure and 11.8 +/- A 4.1 A mu g/24 h (TMSe elim.: 10.8 +/- A 4.6 A mu g/24 h; non-TMSe elim.: 12.6 +/- A 4.2 A mu g Se/24 h) after selenized yeast exposure. Methyl-2-acetamido-2-deoxy-1-seleno-beta-d-galactopyranoside (SeSug1) was the main metabolite in all urine samples, whereas TMSe was another main metabolite in TMSe eliminators' urine. After selenite exposure, a small amount of the dose (0.5 +/- A 0.2 %) was oxidized to selenate and rapidly excreted via urine. With the exception of selenite exposure in TMSe eliminators, the comparison of total Se and the sum of quantified Se species revealed a high renal portion of unidentified species. The study indicated a different metabolism of inorganic and organic Se compounds in human, but also crucial differences of Se metabolism in TMSe eliminators and non-TMSe eliminators.