We assessed the consequence of loss of Cbp on the erythroid compartment in vivo. Epo-responsive cells isolated from Cbp-knockout mice exhibited altered signaling. Cbp loss elevated Lyn activity, promoting the activation of downstream pathways. Loss of Cbp results in an increased viability and enhanced differentiation in vitro. There was an altered erythroblast differentiation profile in the bone marrow of male Cbp–/– mice.