The ability of dividing and non-dividing cells of the avian erythropoietic series to phosphorylate ["Hjdeoxythymidine and [*H]uridine has been studied. Enzyme levels of deoxythymidine kinase were also assayed. Both dividing and immature non-dividing erythroid cells phosphorylated uridine to undine triphosphate (UTP). However, only cells able to synthesize DNA could phosphorylate deoxythymidine ...