Effect of Isopropyl Methane Sulphonate (IMS) on Haemopoietic Colony‐Forming Cells

S ummary . A dose of isopropyl methane sulphonate (IMS) has been selected which depletes the population of CFU in the femur to 30–50%. During the subsequent 5–7 days the surviving population declines to between 0.5% and 2% of controls. It is shown that the IMS‐treated host is a satisfactory environment for growth of CFU in grafts from either normal or IMS‐treated donors although the grafts themselves behave differently from each other. The colonies produced from marrow from IMS‐treated donors are virtually devoid of CFU, whereas 70% of those from control donors contain CFU. It is proposed that IMS, at the dose selected, kills primary, self‐maintaining CFC but does not kill the derived non‐self‐maintaining cells which, nevertheless, are also capable of spleen colony formation. It is suggested that the chemical provides a useful tool for the study of the haemopoietic stem cell complex.