Green onions (Allium fistulosum) enriched with 10 or 100 mu g mL(-1) Se(IV) or SeMet were analyzed for total selenium and species distribution. Anion and cation exchange chromatographies were applied for the separation of selenium species with mass spectrometric detection. Two different sample preparation methods (NaOH and enzymatic) were compared from the Se extraction efficiency point of view. Total selenium concentration accumulated by the onions reached the 200 mu g g(-1) level expressed for dry weight when applying SeMet at a concentration of 100 mu g mL(-1) as the source of Se. Speciation studies revealed that both in onion bulbs and leaves the predominant form of organic selenium is Se-methylselenocysteine (MeSeCys). When Se(IV) was applied for Se-enrichment at a concentration level of 100 mu g mL(-1) both onion leaf and bulb contained a significant amount of inorganic selenium. An unknown compound was also detected. (c) 2006 Elsevier B.V. All rights reserved.