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A sensitive and reliable method using capillary zone electrophoresis with UV-diode array detection has been developed and validated for trace determination of residues of sulfonylurea herbicides in environmental water samples and grapes from different origins. The analytes included are triasulfuron, rimsulfuron, flazasulfuron, metsulfuron-methyl, and chlorsulfuron. Optimum separation has been achieved on a 48.5-cm x 50-mu m (effective length 40 cm) bubble cell capillary using 90 mM ammonium acetate buffer, pH 4.8, by applying a voltage of 20 kV at 25 A degrees C and using p-aminobenzoic acid as the internal standard. In order to increase sensitivity, large volume sample stacking with polarity switching has been applied as on-line preconcentration methodology. For water samples, a solid-phase extraction (SPE) procedure based on the use of Oasis HLB cartridges was applied for off-line preconcentration and cleanup. For grape samples, the SPE procedure was achieved with C-18 sorbent, after extraction of the compounds with MeOH:H2O (1:1) by sonication. The limits of detection for the studied compounds were between 0.04 and 0.12 mu g/L for water samples and 0.97 and 8.30 mu g/kg in the case of grape samples, lower in all cases than the maximum residue limits permitted by the EU for this kind of food. The developed methodology has demonstrated its suitability for the monitoring of these residues in environmental water and grape samples with high sensitivity, precision, and satisfactory recoveries.