A new method based on single-drop microextraction (SDME) combined with electrothermal vaporization atomic absorption spectroscopy (ETV-AAS) was developed for the trace determination of mercury in water samples. A microdrop of m-xylene was applied as the extraction solvent. After extraction, the microdrop was introduced, directly, into a graphite furnace of AAS. Some important extraction parameters such as type of solvent, volume of solvent, sample stirring, ionic strength, sample pH, chelating agent concentration, sample temperature, and extraction time were investigated and optimized. The highest possible microdrop volume of 10 mu L, a sampling temperature of 27 degrees C, and use of m-xylene containing dithizone, as complexing agent, are major parameters led to achieve a high enrichment factor of 970. Under the optimized conditions, the detection limit of the method was 0.01 mu g L-1 and the relative standard deviation was 6.1% (n = 7). The proposed method has been successfully applied to the determination of Hg in two river water samples. The effects of interfering species Such as Pt, Pd, Cu, Au, and Bi, having the tendency to form complexes with dithizone. at two concentration levels of 100 and 1000 mu g L-1 were also studied. (C) 2008 Elsevier B.V. All rights reserved