A liquid-phase microextraction method for the determination of trihalomethanes (THMs) including chloroform (CHCl3), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3) in water samples was developed, with analysis by gas chromatography-electron capture detection (GC-ECD). After the determination of the most suitable solvent and stirring rate for the extraction, several other parameters (solvent drop volume, extraction time and ionic strength of the sample) were optimized using a factorial design to obtain the most relevant variables. The optimized extraction conditions for 5 mL of sample volume in a 10 mL vial were as follows: n-hexane an organic solvent; a solvent drop volume of 2 microL; an extraction time of 5.0 min; a stirring rate of 600 rpm at 25 degrees C; sample ionic strength of 3M sodium chloride. The linear range was 1-75 microg L(-1) for the studied THMs. The limits of detection (LODs) ranged from 0.23 microg L(-1) (for CHBr2Cl) to 0.45 microg L(-1) (for CHCl3). Recoveries of THMs from fortified distilled water were over 70% for a fortification level of 15 microg L(-1), and relative standard deviations of the recoveries were below 5%. Real samples collected from tap water and well water were successfully analyzed using the proposed method. The recovery of spiked water samples was from 73% to 78% with relative standard deviations below 7%.