Hayflick's hypothesis: an approach to in vivo testing

The experimental evidence relating to the hypothesis of finite cellular life is reviewed. It is emphasized that even if somatic cell production were limited its total potential would have to be vast to provide for extensive cellular regeneration. The actual limit of reproductive cell life would therefore not likely be reached in a normal life-span. It is proposed to test the hypothesis by deliberate exhaustion of stem-cell reserve, and iron-55 cytocide is described as an experimental system that might be applicable.