The bioavailability of rifampicin (RIF) in a fixed dose combination (FDC) used for the treatment of tuberculosis remains an area of clinical concern and several pharmaceutical alternatives are being explored to overcome this problem. The present study presents a pharmacological approach in which the bioavailability of a drug may be modulated by utilizing the herb-drug synergism. The pharmacokinetic interaction of some herbal products and a pure molecule isolated fromCuminum cyminumwith RIF is shown in this paper. An aqueous extract derived from cumin seeds produced a significant enhancement of RIF levels in rat plasma. This activity was found to be due to a flavonoid glycoside, 3',5-dihydroxyflavone 7-O-β-D-galacturonide-4'-O-β-D-glucopyranoside (CC-I). CC-I enhanced theCmaxby 35% andAUCby 53% of RIF. The altered bioavailability profile of RIF could be attributed to a permeation enhancing effect of this glycoside. Copyright © 2006 John Wiley & Sons, Ltd.