A fast and accurate method of pre-treatment for biological materials in the hydride generation-atomic absorption spectroscopy (HG-AAS) selenium determination is described. All procedures of sample pre-treatment were performed in closed-vessels in a microwave oven. After sample decomposition using a HNO3/H2O2 mixture, the pre-reduction and a 'denitrification' step (reduction of interfering nitrogen intermediates) with amidosulfuric acid were combined. Hence, analysis time and the risk of element losses or the emergence of possible contamination are minimised.