Abstract: The simultaneous determination of arsenic (As(III), MMAs, DMAs, As(V)) and selenium (Se(IV), Se(VI)) species has been carried out by three instrument combinations. High performance liquid chromatography (HPLC) is coupled with two independent atomic fluorescence spectrometers (AFS) supplied with boosted discharge hollow cathode lamp (BD HCL) by high efficiency sample introduction systems. The efficiency of ultrasonic nebulisation (USN), hydraulic high pressure nebulisation (HHPN) and hydride generation (HG) was compared. The separation of the six species in one system is achieved by gradient elution programs. The HPLC-HG-AFS system provides the best detection limits, but it is not suitable for the direct determination of Se(VI). The HPLC-HG-AFS system was applied for the measurement of arsenic contaminated natural ground water samples. Absolute detection limits of 1.0, 0.5, 1.0, 0.3 and 0.7 pg for Se(IV), As(III), DMAs, MMAs and As(V), respectively, were obtained for a 100 µl injection volume using the HPLC-HG-AFS system.