[Comparison of 2 methods of studying polypotent hematopoietic cells]

The cells giving rise to colonies in the spleen of a lethally irradiated recipient after their transplantation (exogenous CFUs) have a higher self-maintaining ability than those that repopulate their own hemopoietic territory after irradiation, due to the migration of these cells from screened territories (endogenous CFUs). The number of exogenous CFUs and their self-maintaining ability do not change with animals ageing.