A very sensitive and selective spectrofluorometric method has been developed for Hg(II) determination in pharmaceutical and environmental samples. The method is based on measuring the decrease in fluorescence intensity of murexide after binding Hg(II). The intensity of the fluorescence emission peak was measured at ex/em 335/435 nm in several buffer solutions (acetic acid/acetate, NaH2PO4/Na2HPO4, NH4+/NH3) targeting the pH interval 3.0-9.0. The fluorescence intensity decrease was found to be linear in the concentration range of 8 x 10(-7) to 1 x 10(-5) M of Hg(II) by using 5 x 10(-5) M murexide in 0.1 M acetic acid/acetate buffer at pH 4.2. The detection limit was 2 x 10(-7) M. This method was found to be almost free of interference from large excesses of 40 cations and anions. The method was successfully applied to the analysis of Hg(II) in synthetic mixtures, pharmaceutical preparations, and wastewater samples. The recovery was quantitative and the standard deviation for 10 replicates of a sample containing 1 x 10(-6) M Hg(II) was lower than +/-4%.