Analysis of globin mRNAs by primer extension in 7 patients with β-thalassemia (patients no. 1 through 7), 1 patient with sickle cell anemia (patient no. 8), and a normal adult subject (NS). Samples obtained before therapy and during therapy are designated with − and + above the lane, respectively. Patient no. 5 was analyzed before therapy was completed (−), 24 hours after therapy was completed (+), and 44 hours after therapy ended (−*). Fold increases of γ-globin over the subject’s baseline are shown at the bottom of the lanes. Patient no. 4 was the single subject studied in whom an increase in γ-globin mRNA was not observed.