Dihydroergotoxine is a mixture of semi-synthetic ergot alkaloids mainly used for age-related cognitive impairment. In this study, dihydroergotoxine (30 mu M) was added to incubates of rat and bovine liver microsomes, and the resulting major metabolites were identified as hydroxydihydroergocornine, hydroxy-dihydroergocryptine and hydroxy-dihydroergocristine on the basis of molecular mass measurements, determined with a time-of-flight mass spectrometer. The relevance of these to humans was then investigated by simultaneously monitoring dihydroergotoxine and its hydroxy-metabolites in human plasma by LC-MS/MS after oral dosing of dihydroergotoxine mesylate (27 mg) to a healthy volunteer (male, age 45, height 1.93 m, weight 103 kg). In this preliminary approach, the peaks (C-max) of dihydroergocornine, dihydroergocryptine and dihydroergocristine were about 0.04 mu g/l. The peaks (C-max) of their hydroxy-metabolites were 0.98, 0.53 and 0.30 mu g/l, respectively. In conclusion, in this preliminary approach it was found that hydroxy-dihydroergocornine, hydroxydihydroergocryptine and hydroxy-dihydroergocristine were one order of magnitude higher in concentration than their parents in human plasma. Copyright (C) 2007 John Wiley & Sons, Ltd.2911728