A group of pesticides with different chemical structures was determined in water by on-line coupling of solid-phase extraction to gas chromatography with mass spectrometric detection through an on-column interface. A 10 mm x 2 mm I.D. precolumn packed with PLRP-S was selected for the solid-phase extraction process. The parameters affecting the transfer of the analytes from the precolumn to the GC system (e.g. flow-rate, temperature and solvent vapor exit time) were optimized. An organic modifier was added to the sample before the extraction process to avoid adsorption problems. The use of the MS detector under selected ion monitoring acquisition enabled the analytes to be quantified at sub microgram-per-litre levels preconcentrating only 10 ml of sample, and the limits of detection (S/N = 3) were between 2 and 20 ng l-1. The method was applied to the determination of the pesticides in tap and river water, and molinate was determined in Ebro river water.