Interest in the potential medical use of naturally occuring chemicals in plants is increasing. This is intended to provide a comprehensive and up- to-date directory of plants and the substances found in them. It covers over 8000 plant species. This dictionary, which covers the literature up to the end of 1987, is intended to provide this information in a readily accessible form. Each plant is listed alphabetically according to genus and species. Wherever possible, the original papers have been consulted and references to these are given for each class of compound.