Analytical determination by HPLC of five taxanes-paclitaxel, cephalomannine, 10-deacetylpaclitaxel, 10-deacetylcephalomannine and taxcultine-in extracts from the bark of Taxus baccata indicates that taxane concentrations vary seasonally. The highest concentration was found in October and the lowest in January for all taxanes examined. Copyright (C) 1999 John Wiley & Sons, Ltd.