(A) Percent change in HbF %, from week 0 set at 0 %. In patients who were treated with sildenafil, rising by 7.5±11.7% at week 10 (n=8, plotted from week -6, solid black line, p<.05), but not in patients treated with L-arginine (solid grey line, n=6, dropping by 2.9±16% at week 12, p=n.s.). (B) Percent change in F-cell % from week 0, set at 0 %. In patients on sildenafil rising by 6.8±13.1% at week 12 (n=7, plotted from week 0, solid black line, p=n.s.) and in patients on L-arginine diminishing by 2.6±15.7% at week 12 (n=6, solid grey line, p=n.s.).