Plants are one of several novel hosts that can be used for the production of recombinant biopharmaceuticals such as cytokines, hormones, monoclonal antibodies, enzymes and vaccines. The novelty of this technology and its wide range of potential applications require an assessment of possible regulatory concerns in the clinical development of plant-derived biopharmaceuticals. General principles extrapolated from experience gained with biotechnology products from other sources can serve as a foundation to develop scientifically sound strategies for the large-scale production and clinical development of safe and effective biopharmaceuticals in plant hosts.