Since the discovery of Taxol and of its antitumor activity a number of chemical, pharmacological and clinical studies have been performed on this natural diterpene isolated from the genus Taxus. Because the extraction of Taxol from the bark is expensive, difficult and damaging to the Taxus species, alternative sources have been studied. To date, one of the most promising alternatives is the semisynthesis of Taxol from 10-deacetylbaccatin III, a renewable precursor found in the needles of the European yew tree, Taxus baccata. From this natural compound, a number of new active compounds bearing different substituents at carbons 2, 4, 5, 7, 10, 13, 2' and 3' have been prepared. Among the new substances, Taxotere (N-debenzoyl-N-tert-butoxycarbonyl-10-deacetyltaxol) was found to be one of the most potent in its interaction to the cellular target of antitumor taxoids: tubulin. The chemistry and structure-activity relationships of the antitumor taxoids are presented.