A study of different multi-residue methods for the determination of pesticides in groundwater samples was made by comparing several extraction procedures which included liquid-liquid partitioning and solid-phase extraction. The effect of extraction conditions, such as organic solvent, volume ratio, addition of NaCl and pH, were studied. Recoveries, detection and determination limits, as well as precision of the procedures for several replicates were obtained. The pesticides studied were selected taking into account their application on citrus groves in the Plana of Castellon (Spain). These compounds included organochlorine pesticides (lindane, dicofol, chlorfenson and tetradifon), organophosphorous (dimethoate, fenitrothion and methidathion) and phenoxyacid herbicides (MCPA and 2,4-D). Analysis were carried out by high resolution gas chromatography using a dual detection system (ECD and NPD), as well as by high performance liquid chromatography (HPLC) with UV detection. This procedure was applied to several groundwater samples from Castellon province (Spain).