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A tandem mass spectrometric (ms/ms) method using desorption chemical ionization is described for the quantitation of taxol [1], cephalomannine [2], and baccatin III [3] found in Taxus brevifolia bark and needle extracts. A parent ion scan was used to simultaneously determine the weight percentages of 1-3 in bark and needle samples by the method of standard addition. In an alternative experiment, the concentration of 1 in the same samples was determined by ms/ms using trideuterated 10-acetyltaxol [7a] as an internal standard. High-performance liquid chromatography (hplc) was also used to determine the weight percentages of 1-3 in the same T. brevifolia bark and needle extracts with an external standard. The ms/ms method of quantitation by internal standard is the best overall method of analysis examined. With this method, 1 was quantitated in the T. brevifolia extracts at the low picomole level with a relative standard deviation of 17% or better for all samples analyzed with an analysis time of less than five min per sample. The precision, level of quantitation, and speed of analysis of the three methods of taxane quantitation are compared.