Although plants were once the source of most biomedicines, for the past 40 years industry, except in the field of antibiotics, has relied primarily on synthesised new compounds. Relative failures of drug discovery programmes, among other factors, have led to increased interest in plant sources. The absolute minimum cost of meeting all the regulatory requirements - even for a safe, plant-derived compound - is about US $100 million. Investment in a plant-derived drug will therefore be made only if this level of investment can be justified. To be successful as a source of raw material for manufacturing a drug, the active constituent should not be readily synthesised and should have multiple isomers with only one being biologically active and found in pure form in the plant. In turn, the plant - possibly with some modification should be capable of providing the required amounts of the drug in a form that is relatively easily extracted. Gamma-linolenic acid, derived from the oil of evening primroses Oenothera spp. (Onagraceae) and other plants, is used to illustrate the problems and opportunities.