In this work, liquid chromatography-electrospray ionization tandem ion-trap mass spectrometry (LC-MS(n)) was used to investigate the in-vivo and in-vitro metabolism of tectoridin. After oral administration of a single dose (100 mg kg(-1)) of tectoridin to healthy rats, faeces and urine samples were collected for 0-48 h and 0-24 h, respectively. Tectoridin was also incubated with rat intestinal flora and rat liver microsomes. Samples from in-vivo and in-vitro metabolism studies were purified using a C(18) solid-phase extraction cartridge, then separated using a reverse-phase C(18) column with methanol/ water (30:70, v/v, adjusted to pH 10.0 with ammonia water) as mobile phase and detected by an on-line MS(n) system. The structure of the metabolites was elucidated by comparing their molecular weights, retention times and full-scan MS(n) spectra with those of the parent drug. The results revealed six metabolites of tectoridin in urine (tectorigenin, hydrogenated tectorigenin, mono-hydroxylated tectorigenin, di-hydroxylated tectorigenin, glucuronide-conjugated tectorigenin and sulfate-conjugated tectorigenin); three metabolites in faeces (tectorigenin, di-hydroxylated tectorigenin and sulfateconjugated tectorigenin); one metabolite in the intestinal flora incubation mixture (tectorigenin), and four in the liver microsomal incubation mixture (tectorigenin, hydrogenated tectorigenin, mono-hydroxylated tectorigenin and di-hydroxylated tectorigenin). Except for tectorigenin, all other metabolites of tectoridin are reported for the first time.