Se speciation was performed in 24 individual paired serum and cerebrospinal fluid (CSF) samples from neurologically healthy persons. Strong anion exchange (SAX) separation, coupled to inductively coupled plasma–dynamic reaction cell–mass spectrometry (ICP-DRC-MS),was employed. Species identification was done by standard matched retention time, standard addition and by size exclusion chromatography followed from SAX (2-D SECSAX-ICP-DRC-MS) and by SAX followed from CE-ICPDRC-MS (2-D SAX-CE-ICP-DRC-MS). Limit of detection (LoD, 3×standard deviation (SD) of noise) was in the range of 0.026–0.031 μg/L for all investigated species and thus was set uniformly to 0.032 μg/L. Quality control for total Se determination was performed by analysing control materials “human serum” and “urine”, where determined values met target values. Several Se species were found in both sample types having following median values (sequence: serum/ CSF, each in μg Se/L): total Se, 58.39/0.86; selenoprotein P (SePP), 5.19/0.47; Se-methioni