With the help of a previously devised model of cultured cell growth kinetics it was shown that the "plateau" level on the growth curve of human embryo diploid fibroblasts increased, if the cells were grown with Epigid geroprotector-antioxidant (equal results with two drug concentrations: 10(-5) and 10(-7) M, resp.). It was also found that the "plateau" level on the growth curve of cultured "3 days aged" Chinese hamster cells (subcultivated to a fresh medium 3 days after a 1:6 subcultivation) lays higher than the "plateau" level of "14 days aged" cells but lower than that of "7 day aged" cells. Furthermore it was shown that an increase in inoculation density of Chinese hamster cells increased proportionately the rate of cell population growth but had a little effect on the "plateau" level of the growth curve. The data obtained are discussed in terms of some "proliferative" theories of cellular ageing.