Background: The present study was aimed at comparing two techniques of selenium (Se) determination in serum/plasma samples: inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption (GF-AAS). Materials and methods: Blood samples were collected by venipuncture, using Venosafe® closed blood sampling system. The samples were centrifuged. The measurements were performed by Elan DRC-e mass spectrometry, Perkin Elmer, SCIEX, USA and Unicam Solar 989 QZ atomic absorption spectrometry. Reference material, Clincheck® Serum Control Level 1 (Recipe, Germany), was used to verify the determinations. The Laboratory participates in external quality control (G-EQUAS). Results: Analytical parameters for both techniques are respectively: ICP-MS - precision 5.9%, limit of detection 0.19 μg/l, repeatability 5.5%, trueness 2.4%, bias 97.6%, GF-AAS - precision 8%, limit of detection 3.4 μg/l, repeatability 7.2%, trueness 6.8%, bias 93.2%. Conclusions: The benefits of the ICP-MS technique are high accuracy, low detection limits and the possibility of multi-element analysis.