A sensitive atomic fluorescence system for the determination of mercury was optimized. The system consists of a continuous-flow mercury vapour generator coupled to a fluorescence spectrometer specific for mercury. A new gas-liquid separator was developed. A detection limit of 0.9 ng Hg l-1 was obtained. The system was combined with a microwave oven for dissolving samples in closed Teflon PFA vessels. Accurate results were obtained for certified reference materials, and biological samples such as urine and hair were analysed.