A method is described for the determination of lamotrigine in serum or plasma, based on gas chromatography with nitrogen-phosphorus detection. The method requires minimal sample preparation. The drug is extracted from 1.0 ml of serum at pH 11 into butylacetate containing prazepam as internal standard. An aliquot of the organic phase is then injected onto an HP-5 fused silica capillary column and analyzed with temperature programming from 90 degrees to 250 degrees C. Lamotrigine is characterized by a relative retention time of 0.832 (+/-0.03) compared with prazepam. The method is competitive with the reported high-performance liquid chromatography procedures in terms of precision and sensitivity. Coefficients of variation, calculated from the results of between-run reproducibility tests, were 6.7%, 4.6%, 4.8%, and 6.2% for samples spiked with 0.20, 1.21, 2.42 and 10.84 micrograms/ml lamotrigine, respectively. The lower limit of quantitation of the method is 0.15 microgram/ml. The proposed procedure can be integrated easily in a comprehensive toxicology screening.