Numerous stimuli, including viral infection and deprivation of cell growth factors, can induce apoptosis (programmed cell death) of cells grown in culture. The genetic machinery that controls the apoptotic response is currently being investigated. The expression of genes involved in this process using recombinant DNA technology has been utilized to control and limit programmed cell death in cultured cells. In the future, this technology may be used to increase the productive lifetime of cell culture systems.