Abstract Supplementation of glucose at the beginning of the plateau phase has been shown to extend the duration of this phase by as much as fourfold in suspension cultures of L-M strain mouse cells in a protein-free medium. The role of glucose seems to be, at least in part, one of sparing action on the cells by providing a readily available energy source. Continued cell synthetic activity also may be promoted. No net increase in cell numbers occurred. Decrease in the average cell size and loss of viability were significantly delayed while a cyclic pattern of cell size changes suggested a low level of population turnover and renewal.