A highly sensitive flow-injection spectrofluorimetric method is presented for the rapid and simple determination of Hg (11) in environmental and pharmaceutical samples. Murexide (ammonium purpurate) was used as the fluorescence reagent in the carrier stream. An emission peak of murexide, which is decreased linearly by addition of Hg (11), occurs at 435 nm in aqueous solution with excitation at 335 nm. A linear calibration was obtained for 5-200 ng ml(-1) Hg (11) with the relative standard deviation 2.5% (n=5) for a 20 mu l injection volume Hg (II). The limit of the detection was 1 ng ml(-1) and the sampling rate was 80 h(-1). No significant interference was found by the ions commonly found in the most environmental samples. The proposed method was successfully applied for the determination of trace mercury in real samples and the validation of the proposed methodology is provided.