['Traditional Chinese medicine (TCM) has become very popular in Western countries during the last years. Zicao, a remedy of TCM, has been traditionally used to treat cancer, and, its main constituents, naphthoquinones, have been reported to possess antitumor activity (Chen et al., 2002; Papageorgiou et al., 1999). Here, we prepared extracts of different polarities of Onosma paniculatum Bur. & Franch., a plant which is amongst others used as Zicao, but, much less investigated. The extracts were analyzed concerning their growth inhibitory and apoptosis-inducing activity in various tumor cells.', 'Cell viability was measured by XTT viability and a growth inhibition assay. Effects on the cell cycle and caspase-3 were determined by flow cytometry.', 'From three different extracts, a petrol ether extract showed significant growth inhibitory effect, cell cycle influence and caspase-3 dependent induction of apoptosis which was time and dose dependent.'] Does a petrol ether extract of the roots of Onosma paniculatum induce cell death in a caspase dependent manner?