A validated HPLC method for the determination of 11-keto-beta-boswellic acid (KBA) in human plasma was developed. The method involves the solid-phase extraction of KBA from plasma followed by a separation with reversed-phase HPLC. Calibration was based on external standardisation and ranged between 0.1 and 2.0 microg KBA per ml plasma. Linearity was established over the entire calibration range and in each case the coefficient of correlation (r2) was above 0.99. The recovery of KBA from plasma was 85.7%. It was further demonstrated that the method can be applied successfully to monitor the level of KBA in plasma.