A complexometric method for the determination of mercury(II) in presence of other metal ions is described based on the selective masking action of 2-mercaptopropionic acid towards mercury(II). Mercury(II) present in a given sample solution is first complexed with an excess of EDTA and the unreacted EDTA is titrated against zinc sulphate solution at pH 5-6 (hexamine buffer) using xylenol orange as the indicator. A 0.5% aqueous solution of 2-mercaptopropionic acid is then added to displace EDTA from the Hg(II)-EDTA complex. The released EDTA is estimated. Reproducible and accurate results are obtained for 4-88 mg of mercury(II) with relative error less than +/- 0.46% and coefficient of variation not more than 0.34%. The effects of various ions were studied. The method is used for the analysis of mercury in its synthetic alloy mixtures and also in complexes.