Aqueous solutions and blood plasma spiked with selenite (Se(IV)), selenate (Se(VI)), selenomethionine (SeMet) or trimethylselenonium (TMSe) iodide were analyzed by Zeeman-corrected electrothermal atomic absorption spectrometry (ETAAS) using palladium as a chemical modifier, and by inductively coupled plasma mass spectrometry (ICP-MS). Using ETAAS, the sensitivities for Se(IV), SeMet and TMSe in aqueous solution were similar, whereas the sensitivity of Se(VI) was 63% of that value. In blood plasma, the ETAAS sensitivities of Se(IV) and Se(VI) were equal, whereas the sensitivities of SeMet and TMSe were 87 and 56%, respectively, of that value. In contrast, the ICP-MS sensitivities obtained for Se(VI), TMSe and SeMet were between 96 and 98% of that obtained for Se(IV) in aqueous solution and in blood plasma. It is concluded, that ICP-MS is superior to ETAAS as the problem of differences in sensitivity of the selenium species when using ETAAS are not prevalent when using the ICP-MS technique. (C) 1998 Elsevier Science B.V. All rights reserved