In the course of a chemotaxonomical screening project, identified plant material of H. procumbens and H. zeyheri, collected on different sites in southern Africa, was investigated by reversed phase HPLC anal. The investigation indicated a high variability of the genus Harpagophytum, which is reflected in a wide range of harpagoside/8-p-coumaroyl-harpagide ratios. This variability of ratios may interfere with quality evaluations of pharmaceutical drug material, whereas the calculation of this ratio can still be regarded as a valuable tool for the taxonomical identification of plant material. For the detection of adulterations with H. zeyheri in pharmaceutical drugs, a limiting value of 8% 8-p-coumaroyl-harpagide within the total iridoids is suggested.