Baseline and 2-year HbF (A and B) and F-cell (C and D) values in placebo-assigned and HU-treated patients. Baseline values (X-axis) and 2-year values (Y-axis) along with their regression lines are shown for the HU-assigned (B and D) and placebo-assigned (A and C) groups. Only in the HU-assigned patients is there an increase in HbF (B) and F cells (D).