AbstractMolecules in conditioned medium from stimulated lymphocyte populations or from certain cell lines are known to stimulate cells committed to various hemopoietic lineages as well as pluripotential cells to form colonies in culture. In this study, the relationship between molecules active on pluripotential cells and early cells committed to granulocyte, macrophage, megakaryocyte, or red cell production was explored using techniques of chemical separation. After separation on the basis of charge, or after sequential purification using methods of high resolving power based on hydrophobicity and size, these activities remained associated with one another. The observations provide support for a model which proposes that pluripotential hemopoietic precursor cells as well as their early committed progeny may all be responsive to a single lineage‐indifferent factor. Responsiveness to “lineage‐specific” factors such as erythropoietin is proposed to be a feature only of later cells after they have made the appropriate receptors as part of their differentiation