The iridoids of Harpagophytum procumbens and Harpagophytum zeyheri were studied by CLHP. Harpagoside is the main iridoid for both drugs whereas 8-p-coumaroylharpagide is a representative iridoid of Harpagophytum zeyheri only. The ratio harpagoside/8-p-coumaroylharpagide can be used to distinguish chemically both species. For commercial dried aqueous extracts this ratio is intermediate because they are probably prepared from a mixture of H. procumbens and H. zeyheri drugs. The aqueous extracts of both drugs show similar analgesic and anti-inflammatory properties. Harpagophytum procumbens and Harpagophytum zeyheri should be accepted as sources for the drug Harpagophyti radix.