Synergy is normally assumed to play a part in the medicinal effects of plant extracts, and is considered to be one of the greatest assets of phytotherapy. Medical herbalists have always claimed that whole plant extracts have superior effects over single isolated constituents; it is even claimed that combinations of herbs have synergistic effects. But what precisely is meant by the term synergy, and is there any evidence that it does occur in medicinal plants? These and other questions regarding synergy were addressed by Dr Elizabeth Williamson from the Centre for Pharmacognosy at the School of Pharmacy, University of London, UK, during her presentation at a discussion meeting on phytotherapy held at the Novartis Foundation [London, UK; March, 1999].