Crop plants show great promise as alternatives to more traditional expression systems such as mammalian cells for the production of biopharmaceuticals. Most of the major crops are now amenable to transformation, and increasing knowledge about promoters and targeting sequences is allowing transgene expression to be specifically targeted to storage tissues for easy storage and isolation. Compared with mammalian production systems, plants produce high yields of protein with similar glycosylation levels at a fraction of the cost. Seed-specific expression often results in significant yields of stable protein, reducing shipping and storage costs. Expression in tubers or fruits should also facilitate the production of edible vaccines (see, for example, pp. 1167 —Mason). Problems remain, however, with transgene silencing, and more information on mRNA stability is required to achiever higher/consistent levels of expression. On page 1151, Giddings et al. summarize current progress in the production of protein and peptide pharmaceuticals in plants, outlining the main types of expression systems and products currently under development.