A method for the determination of free and conjugated triclosan at concentrations as low as 2 ng/ml in human plasma or urine is described. Conjugated metabolites are split by enzyme hydrolysis. After addition of an internal standard, triclosan is extracted at acid pH into petroleum ether, transferred to an alkaline aqueous solution, and back-estracted into petroleum ether after acidification. Both compounds are acetylated with acetic anhydride in the presence of pyridine. The acetyl derivatives are determined by GLC using a 63Ni-electron-capture detector.