Headspace-solid-phase microextraction (HS-SPME) combined with gas chromatography-electron capture detector (GC-ECD) has been developed and studied for the determination of trihalomethanes (THMs) in treated water samples. Experimental parameters such as the selection of thickness of the polymer coating, addition of salt, magnetic stirring, extraction temperature, and extraction time were studied. Extraction of the analytes was performed using HS-SPME with a 100 mu m poly(dimethylsiloxane) coating followed by thermal desorption at 250 degrees C and GC analysis. The optimized conditions were 20 min extraction time at 35 degrees C with 25 w/v% NaCl. Analytical parameters such as linearity and limit of detection were also evaluated. The linear range of 1-100 mu g/l was established with relative standard deviations (%RSD) within the range, 1.3-11.7%. The limits of detection (LODs) were ranged from 1.4 ng/l to 6.1 ng/l. The average THM concentration was 88.16 mu g/l which was well within the proposed European Union directive of 100 mu g/l. (C) 2009 Elsevier B.V. All rights reserved.