Of 13 patients with normalized velocities on transfusion, 10 had normal MRAs, and transfusion therapy was replaced with hydroxyurea. Four of these 10 patients redeveloped high velocities, so only 6 remained transfusion In another study, the adjusted mean change in TCD velocities was 13.0 cm/s (95% CI, 20.19 to 5.92) in a hydroxyurea-treated group and 4.72 cm/s (95% CI, 3.24 to 12.69) in control subjects (P<0.001).587 In a study of 59 initiat- ing hydroxyurea therapy for severe vaso-occlusive complica- tions who had pretreatment baseline TCD measurements, 37 had increased time-averaged maximum velocities 140 cm/s and were enrolled in a trial with TCD velocities measured at maximum tolerated dose and 1 year later.588 At the hydroxy- urea maximum tolerated dose (mean SD=27.9 2.7 mg/kg per day), decreases were observed in bilateral middle cerebral artery velocities. The magnitude of the TCD velocity decline correlated with the maximal baseline TCD value.588 Most recently, the phase III Pediatric Hydroxyurea Clinical Trial (BABY HUG) demonstrated significantly lower increases in TCD velocities in the hydroxyurea group, but neurocognitive testing of the infants was not statistically different between The SWiTCH study, a phase III noninferiority trial comparing standard treatment (transfusions/chelation) with alternative treatment (hydroxyurea/phlebotomy) for chil- dren with SCA, stroke, and iron overload,579 was stopped for safety reasons when adjudication documented no strokes in patients on transfusions/chelation but a 10% stroke rate in patients on hydroxyurea/phlebotomy. Hydroxyurea therapy for stroke prevention is promising for primary stroke preven- tion but requires additional study. Results from the ongo- ing Transcranial Doppler With Transfusions Changing to Hydroxyurea (TWiTCH) trial may provide greater insight into the benefit of hydroxyurea in stroke prevention. Bone marrow transplantation is usually entertained after stroke, but TCD and other indexes of cerebral vasculopathy have also been used as an indication for myeloablative stem- cell transplantation. 