An automatic flow injection (FI) system for the determination of mercury was developed using a commercial Gold vapour atomic absorption spectrophotometer (CVAAS). Control and data acquisition in the FI system was done with an IBM-PC 286 XI compatible microcomputer and a home-made interface, using software written in QuickBasic 4.5. Mercury content was determined by: sampling using a combination of four electromechanical three-way poly(tetrafluoroethylene) valves; separation of the dissolved reduced mercury in a gas/liquid separation cell using nitrogen as carrier, followed by amalgamation of the stripped metal on a gold wire column; after stripping the metal, cleaning the separation cell using vacuum, which was controlled by a three-way electromechanical valve; heating the gold wire column automatically to release the amalgamated mercury using an external nichrome wire coil; storing the output signals automatically to calculate the final mercury concentration, using commercially available software. The optimized system presents a detection limit of 5.3 ng l(-1) of mercury (30 pg absolute) using 5.7 ml (three injections of 1900 mu l of the sample) with an analytical frequency of six samples per hour and reproducibility of 5%. The procedure was used to determine mercury in fish, hair and natural water samples.186193198