For the determination of pentacyclic triterpenes of the boswellic acid family in human plasma a novel sensitive method was developed combining serial extraction on diatomaceous earth and graphitized carbon black followed by reversed phase high-performance liquid chromatography (HPLC) and photodiode array detection. The overall average extraction yield of 12 different pentacyclic triterpenic acids was approximately 66%. The calibration graphs were linear with coefficients of correlation for all compounds greater than 0.999. The overall within-day and between-day coefficients of variation (CV) for the 12 pentacyclic triterpenic acids were 5.6 and 6.8%, respectively. This HPLC procedure delivers the analytical sensitivity, precision and accuracy required for clinical pharmacokinetic and therapeutic studies.