A wall-coated histidine capillary column was developed for the on-line preconcentration of nonsteroidal anti-inflammatory drugs (NSAIDs) in capillary electrochromatography (CEC). A wide variety of experimental parameters, such as the sample buffer, background electrolyte (BGE) composition, concentration, sample plug lengths, water plug, and the effect of organic modifiers were studied. The relationship between peak height and injection times for the NSAIDs by variation of sample and BGE buffer concentration was investigated. On addition of sodium chloride (0.3-0.6%) to the sample zone, the stacking efficiency was increased. With acetate buffer (100 mm, pH 5.0)/ ethanol (20% v/v) as BGE and sample solution in acetate buffer (0.2 mm, pH 5.0)/ ethanol (20% v/v)/NaCl (0.3% w/v), NSAIDs could be determined at low mum levels without sample matrix removal. The detection limit was 0.096 mum for indoprofen, 0.110 mum for ketoprofen, 0.012 mum for naproxen, 0.023 mum for ibuprofen, 0.110 mum for fenoprofen, 0.140 mum for flurbiprofen, and 0.120 mum for suprofen. The method could be successfully applied to the simultaneous determination of NSAIDs in urine. The recoveries were better than 82% for all the analytes. The present method enables simple manipulation with UV detection for the determination of NSAIDs at low concentration levels in complex matrix samples.