Although a large number of compounds from a wide variety of plants have been tested for antitumor activity, none has played a more vital role in cancer chemotherapy than the vinca alkaloids. These compounds are present in minute quantities in the plant Catharanthus roseus G. Don (Vinca rosea Linn.), commonly called the periwinkle. Although this plant contains in excess of fifty alkaloids, only two of these (vincristine and vinblastine) have become established as important cancer chemotherapeutic agents.