Recent phytochemical and ecological investigations in many parts of the world, including in our laboratories on dehydropyrrolizidine. alkaloids in Compositae, alkaloids and steroidal bitter principles in Solanaceae and various taxins 0f Apocynaceae--Parson--sieae, have revealed a large variability in the. production of diverse mícromolecules which protect plants or serve in their communication. The. qualitative and quantitative plant chemistry varies in accord with immediate and local macroecoloqical conditions, changing continuously through time, space, and the dynamics o$ interretations with other organism. Such a qenetic and physioloqical variability in the chemosynthestic capacities of plants could permit the increase, reduction, or channelinq of energy into bio-synthetic pathways leading to useful pharmaceuticals. It would be best harnessed through detailed studies of the variations possible, coupled with selection of both gene-sets and environmental regimes to optimize the productivity and purity of the desirable substances (Ecological Engineering of medicinal plants).