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Large-scale animal cell cultures are used extensively by the biotechnology and pharmaceutical industries for the production of diagnostic and therapeutic proteins. Recent data suggest that approximately half the profits generated by ‘new’biotechnology companies comes from products derived from animal cell cultures’. Animal cells are also used in a range of quality control and analytical assays. As a result, there has been considerable interest in optimization of production schemes. The main focus has been on developing strategies for optimizing culture conditions for cell growth. The manipulation of culture medium, agitation, aeration levels, and pH, for example, have all led to improvements in cell culture conditions. However, little interest has been shown in controlling the level of cell death, largely because it was thought that cells die by the passive process of necrosis and little could be done to alter this. Within the past few years, it has been demonstrated that under both physiological and in vitro conditions, cells that experience mild