One of the main reasons why there are so few commercial processes which utilize plant cell cultures on a large scale is the cost effectiveness of the maintenance and processing of sterile cultures versus yield. Poor secondary metabolite biosynthesis and culture instability have prevented commercialization of many plant culture systems. Secondary products are frequently produced in cell cultures in lower yield than in the parent plant; however, there are more than 30 examples where the yield of secondary compounds from plant cell cultures is equal to or in excess of that produced by the parent plant (Phillipson 1990). Providing selection for high-yielding cells can be made and stable cultures produced, commercial exploitation may be considered, providing that the market cost of the compound produced allows the process to be cost-effective.