A reversed-phase high-performance liquid chromatographic method is described for the determination of 3-methylhistidine content in human urine using pre-column derivatization with phenylisothiocyanate, isocratic elution with 15 mM sodium acetate-acetonitrile (92:8, v/v) and electrochemical detection. The limit of quantitation was 0.1 pmol. The method has been applied in routine analyses of 3-methylhistidine in both clinical and research work.