The gas chromatographic (CC) analysis of I ,2,3-propenetricarboxylic acid (cis-aconitic acid), a member of the Krebs-cycle acids is normally carried out by esterification usually with methanolt”. Diazomethane has been found to be among the best esterification reagents for carboxylic acids because of quantitative conversion obtainable.at room temperature3. A secondary reaction of diazomethane with unsaturated acids involves its cysloaddition to a carbon-carbon double bond to form a pyrazoline compound. Whereas this reaction is well known for trans-butenedioic acid (fumaric acid) which appears to be stabIe3*’ during GC, little information is available for the pyrazoline compound derived from the aconitate ester. However, McKeown and Bead3 found that cis-aconitic acid was isomerised completely to the trans ester with diazomethane. On prolonged exposure of cisand trans-aconitic acid with diazomethane, no welldefined peak was obtained on a diethylene glycol succinate (DEGS) column._Other workers**2=J reported no apparent difficulty using excess diazomethane in the analysis of the aconitic acid trimethyl ester except for variations in the proportions of the cis and truns forms due to isomerization. This paper presents the results of an examination of the reaction of diazomethane with aconitic acid and its trimethyl ester. It is shown that a pyrazoline derivative is formed in the presence of excess diazomethane and this compound decomposes on chromatographic columns at moderately low temperatures. Depending upon the stationary phase, the various reaction products complicate the analysis of the Krebscycle acids.