Plant-derived compounds have played an important role in the development of several clinically useful anti-cancer agents. These include vinblastine, vincristine, the camptothecin derivatives, topotecan and irinotecan, etoposide, and paclitaxel (Taxol(R)). Several promising new agents are in clinical development based on selective activity against cancer-related molecular targets, including flavopiridol and Combretastatin A4 phosphate. Recently, plants have yielded several agents showing anti-AIDS activity, and one of these, (+)-calanolide A, is in clinical development.