Gas chromatographic (GC) studies with halogen-selective electrolytic conductivity detection (ELCD) showed that chlorinated carboxylic acids are major organochlorine compounds in lipids of eel (Anguilla anguilla) from the receiving waters of a chlorine bleaching sulphite pulp mill. To facilitate the recording of full mass spectra, chlorinated carboxylic acid methyl esters were cold-trapped after capillary GC separation monitored with ELCD. Methyl dichlorooctadecanoate was identified using GC/mass spectrometry (GC/MS) with both electron impact (EI) and ammonia positive-ion chemical ionization (PICI). Methyl tetrachlorooctadecanoate was indicated by GC/EIMS. Each chlorinated fatty acid was observed at two retention times, suggesting the presence of isomers. The original fatty acid methyl esters derived from the eel lipids were subjected to GC/MS in the selected-ion monitoring mode; methyl dichlorooctadecanoate was detected using PICI and methyl tetrachlorooctadecanoate was detected using El ionization.