A simple method for the determination of ultra-trace amounts of germanium in natural waters has been developed. Germanium was preconcentrated using silica having mercapto functional groups, namely mercapto silica and determined by hydride generation flame atomic absorption spectrometry (HGAAS). Utilising mercapto silica, satisfactory recovery values (> 95%) were obtained at natural pH, for germanate concentrations as low as 50 ng 1(-1) Considering the highest preconcentration factor (400-fold) obtained, the sensitivity and 3s-detection limit of mercapto silica-HGAAS system can be expressed as 3.65 ng 1(-1)/0.0044 AU and 0.813 ng 1(-1), respectively. Interference effects of diverse ions were investigated for HGAAS and mercapto silica-HGAAS systems. (C) 2000 Elsevier Science B.V. All rights reserved.