A simple and reliable high-performance liquid chromatographic (HPLC) method with UV-vis detection has been developed and validated for the determination of gabapentin (GBP) in human plasma and urine. The clean up of the sample was carried out by solid-phase extraction with C18-cartridge. After the clean up procedure, the samples were pre-column derivatizated with 1,2-naphthoquinone-4-sulphonic acid sodium salt (NQS). A chromatographic separation was achieved on a C18 column with a mobile phase consisting of acetonitrile and 10 mM orthophosphoric acid (pH 2.5) with isocratic elution (35:65). Baclofen was used as an internal standard (I.S.). The method developed for GBP was linear over the concentration range of 0.05-5.0 mu g/ml and 0.1-10.0 mu g/ml for plasma and urine, respectively. The method is precise (relative standard deviation, R.S.D. < 4.05%) and accurate (relative mean error, RME < 0.15%); mean absolute recoveries were 72.21% for plasma and 72.73% for urine. (c) 2006 Elsevier B.V. All rights reserved.