The proliferative potential of chick embryo fibroblasts: population doublings vs. time in culture.

Chick embryo fibroblasts were maintained in a non-proliferating state up to 150 days in medium containing reduced concentrations of fetal bovine serum. Under these conditions the total time in culture was increased from 50 to 200 days while the total proliferative potential decreased only slightly. From these experiments we conclude that the ability of chick embryo fibroblasts to proliferate in vitro is much more dependent on the number of previous in vitro doublings than on the duration of the time in the culture.