AbstractAn analytical procedure was developed for the determination of methylmercury in human hair using capillary gas chromatography with electron capture detection (GC–ECD). Hair samples are digested in alkaline solution/toluene in an ultrasonic bath at about 50°C. After cooling and treatment with hydrochloric acid (6 mol I−1) and a saturated solution of copper sulphate, the organic phase is extracted with a cysteine solution. Methylmercury is back‐extracted in toluene by adding copper sulphate and potassium bromide and analysed by GC–ECD using a DB17 capillary column. The practical detection limit of the method for methylmercury is 50 ng g−1using 100 mg of hair sample. Column performances and injection reproducibility have been evaluated. Results on 13 samples of human hair are presented and related to the total mercury concentration. The method, consisting of the optimization of similar analytical procedures through improvements in the various steps, allows for sensitive and reliable quantitation of methylmercury in hair with good precision an