The original report of Hiatt (1989) initiated a wave of excitement at the realization that a complex mammalian protein such as immunoglobulin could be assembled within a plant cell. The general reaction was one of amazement, but interest in exploiting the possibilities arising from the discovery, for example to make antibodies of therapeutic value, has taken a considerable time to develop. In the meantime, other recombinant expression systems and traditional cell culture techniques have advanced and overcome some of their problems, particularly those associated with yields. Plants, however, still offer unique advantages, especially in their ability to match the protein assembly capabilities of mammalian cells (as demonstrated by the assembly of SIgA molecules), as well as to provide antibodies in bulk at low cost. In addition, the area of "immunization" of plants holds great promise and will surely be a field of enormous growth for the future.