Submitted March 22, 1996.
Comparison of recent results in studies of telomeres and telomerases, limitation of the proliferative potential of untransformed cell populations ("Hayflick limit"), kinetics and molecular mechanism of cell proliferation and differentiation, and factors determining life span of multicellular organisms leads to the following conclusions: 1) chromosome shortening upon consecutive cell divisions in the absence of telomerase limits cell proliferation beyond the Hayflick limit; 2) the Hayflick limit could arise from a mechanism defining not the lifetime duration of multicellular organisms, but their physical dimensions (to which it is correlated).
KEY WORDS: telomere, telomerase, DNA replication, cell proliferation, cell differentiation, cell transformation, Hayflick limit, lifetime.