Background: Childhood cerebral adrenoleukodystrophy (CCALD), a progressive demyelinating disease affecting school-aged boys, causes death within a few years. Oxidative stress is an important contributing factor. N-acetylcysteine (NAC; 280 mg/kg/day) added as adjunctive therapy to reduced-intensity hematopoietic cell transplantation (HCT) improves survival in advanced cases. However, the mechanisms underlying the benefits of NAC are unclear. Objective: The aim of this study was to understand the mechanism of action of NAC in the setting of HCT in CCALD. Methods: Immunoassays were carried out to determine changes in heme oxygenase-1 (HO-1) and ferritin expression in plasma samples collected from boys with CCALD at three different timepoints during the course of transplantation. In addition, the induction of HO-1 was also confirmed in normal fibroblasts following incubation with 10-100 μmol/L NAC for 4 h. Results: Following NAC therapy we observed an increase in expression of the antioxidants HO-1 (~4-fold) and its effector ferritin (~160-fold) in patient samples as compared with baseline. We also observed that NAC exposure significantly increased HO-1 expression in fibroblasts. Conclusion: Our data suggest that HO-1 is a possible target protein of NAC and a mediator of its cytoprotective effects in these patients.