Glycodeoxycholic acid (GDCA), a bile acid, is formed in the liver from chenodeoxycholate and glycine. GDCA was one of twenty-five plasma metabolites, which were significantly different among asthma and healthy controls. Besides, GDCA was elevated in patients with acetaminophen-induced acute liver failure (AALF) and was significantly increased in non-surviving AALF patients compared with survivors. Thus GDCA level could serve as a prognostic biomarker for AALF patients.