A method for the measurement of malondialdehyde (MDA) using GLC with a nitrogen phosphorus detector (GLC/NPD) is described and evaluated. The method uses 2-hydrazinobenzothiazole (HBT) which forms condensation derivatives with MDA, acetoacetaldehyde, and acetylacetone (AA). GC/MS and 13C NMR studies of the three derivatives obtained showed that they are 2-(pyrazol-1'-yl)benzothiazoles and that they can be separated by GLC/NPD. Any one of these derivatives can be used as an internal standard for the measurement of the other two. The optimal conditions for the measurement of MDA were studied. At pH 2.5 and 70 degrees C, the condensation derivative is quantitatively formed in 30 min. Its extraction is obtained by a mixture of n-hexane/isoamyl alcohol 98/2 (v/v) containing HBT-AA as internal standard. The GLC detection limit is 0.04 pmol. Inter- and intrassay coefficients of variation were 2.9 and an average of 4.0%, respectively. The method is specific, and there was no interference from other carbonyl compounds. The artifactual formation of MDA from carbohydrates during the derivatization reaction is negligible. The method is proposed as a reference method for the standardization of working solutions of MDA or MDA-generating solutions.