Abstract
The influence of cell density on DNA synthesis of human embryonic fibroblasts was studied by measuring the incorporation of tritium-labeled thymidine with autoradiographic techniques. As the inoculum decreased an increased proportion of cells entered the S period during the time between subcultivation and confluency. The amount of labeled cells after subcultivation and after induction of division in stationary cultures was measured. Cells in crowded cultures are delayed in the G1 and G2 periods.