The kinetics of colony formation by CFU-GM in vitro.

Video-recordings of whole normal bone marrow granulocyte-macrophage colony (CFU-GM) cultures were made after 7, 14 and 21 d. Retrospective viewing of the tapes allowed the relationships to each other of the colonies scored on the three different occasions to be documented. The results show that, according to our scoring criteria, there is very little overlap between the numbers of colonies scored on days 7, 14 and 21. Moreover, only about 10% of the progenitors in a sample form day 21 colonies. The remaining progenitors form colonies earlier in the culture period and either disappear before day 21 or remain small.