The dose-dependence of the split-dose response of marrow colony-forming units (CFU-S): similarity to other tissues.

The split-dose effect for survival of colony-forming units (CFU-S) in mouse bone-marrow increases with increasing total dose. This is compatible with the shape of the survival curve, since detailed measurements at doses lower than 200 rad show the presence of a marked initial slope, followed by a tendency towards an increased sensitivity at higher doses. The magnitude of the increase in the split-dose effect is quantitatively similar to values observed by others at comparable low doses in skin, intestine and lung, as deduced from multifraction experiments. It is concluded that these cells do not differ markedly, as has been generally believed, from many other cell types in the ability to demonstrate split-dose effects, when the doses used in the experiments are strictly comparable.