The large-scale or mass cultivation of plant cells is the growth of plant cell suspensions at volumes above those normally produced in shake flasks, that is, above IL. Attempts to grow plant cells in fermenters or bioreactors started in the early 1960s with converted carboys. The area has developed steadily, such that today bioreactors in excess of 5000 L have been used successfully for large-scale plant cell culture (1,2). Much of the early work was carried out using bioreactors designed for microbial culture. It was soon found, however, that although plant cell suspensions appear to be similar in many ways to microbial cultures, there are, in fact, key differences that can have a significant influence on large-scale cultivation. Plant cells are large, 20-40 µM in diameter, and up to 100 PM in length; further, they rarely occur as single cells, but as aggregates of up to 2 mm in diameter (Fig. 1). The individual plant cell soon after division is typically rounded, containing considerable amounts of cytoplasm; however, as it ages, the cell expands and becomes dominated by a large vacuole. In consequence, the overall metabolic activity is low compared with microbial cells, which in turn gives a very slow growth rate (measured in days.