Precise determination of cell cycle length and G(0)-->G(1) transition time of CD4(+) lymphocytes in relation to age was never done before. We show that the cell cycle of healthy elderly donors' CD4(+) cells is significantly shorter, while time to the first division (G(0)-->G(1)) extended compared to cells of young people. The G(0)-->G(1) time inversely correlates with cycle length and the number of CD28 molecules. Quickening of elderly CD4(+) cell divisions depends on overexpression of cyclin D1, possibly related to lowered proteolytic degradation by calpain. Apoptosis eliminates most of responding cells after only one or two divisions, especially in older donors.