Simultaneous analysis of DNA content, adult hemoglobin HbA (α2β2) and fetal hemoglobin HbF (α2γ2) resulted in a robust and sensitive assay, capable of detecting changes at the single cell level in hemoglobinization and in γ/β ratio in response to drugs, as proved by the response of β-K562 to the known γ-globin inducers hemin, hydroxyurea and butyric acid and to two additional HDAC inhibitors: entinostat and dacinostat.