Murine erythroleukemia cells (MELC) are induced to erythroid differentiation by culture with 4 mM hexamethylenebisacetamide. The relationship between onset of accumulation of globin mRNA and cell cycle phase has been examined in MELC fractionated with respect to cell cycle (G1, early S, mid S, and late S/G2) by the technique of centrifugal elutriation. This technique provides synchronized populations of cells without use of chemicals that block cell function (e.g., DNA synthesis). It is shown that the initial onset of accumulation of globin mRNA occurs during the first G1 phase after a complete S traversed in culture with inducer. Once globin mRNA synthesis is initiated, it continues throughout the cell cycle. Studies of synchronized MELC populations exposed to hexamethylenebisacetamide starting in G1, mid S, or late S/G2, provide evidence that an effect of the inducer during G1 or early S is critical to initiation of accumulation of newly synthesized globin mRNA and to the prolongation of G1, both of which are associated with terminal erythroid differentiation.