A novel liquid chromatography-mass spectrometry method has been established for the determination of a newly developed anti-cancer agent epothilone D derivative (Epo D 7-HD) in human plasma. The plasma sample was prepared by liquid-liquid extraction with methanol. Epo D 7-HD was quantitated on a C(18) column with acetonitrile-methanol (80/20, v/v) as mobile phase using LC-MS operating in positive atmospheric pressure chemical ionization with a total run time of 6.0 min. For Epo D 7-HD at the concentrations of 1, 4 and 10 mu g mL(-1) in human plasma, the absolute extraction recoveries were 83.05, 82.37 and 80.09%, respectively. The limit of detection and quantification of Epo D 7-HD was 20 and 100 ng mL(-1), respectively. The linear quantification range of the method was 1-20 mu g mL(-1) in human plasma with linear correlation coefficients greater than 0.999. The intra- and inter-day accuracy for Epo D 7-HD at 1, 4 and 10 mu g mL(-1) levels in human plasma fell in the ranges of 95.61-101.71% and 95.28-99.80%, and the intra- and inter-day precision were in the ranges of 5.59-8.03% and 7.82-11.39%, respectively. This assay was applied to the determination of half-life of Epo D 7-HD in human plasma.