Abstract The 3H-thymidine (3H-TdR) incorporation rate of diploid human embryo lung fibroblast cell (2BS) in old cells was significantly lower than that in middle age cells and young cells. EPidermal growth factor (EGF) stimulated tha 3H-TdR incorporation rates of all three kinds of cells with different age. The results of Northern and dot hybridization showed that the level of HER-2 in old cells was lower than those in young cells. EGF could induce expression of HER-2 gene in young cells but not in old cells. As the cells reached 100% of their life span, the EGFR mRNA decreased obviously.