OBJECTIVE: Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by social communication differences and restricted interests. One proposed biologic mechanism underlying ASD is oxidative stress, leading to the clinical use of glutathione based on anecdotal reports of improved behavior in autistic children. In this pilot study, we tested this observation using a randomized clinical trial format to collect preliminary data on glutathione safety and efficacy. METHODS: Glutathione and glutathione in combination with vitamin C and N-acetylcysteine (Trio) were tested. Both treatments were administered in double-blind placebo-controlled randomized crossover studies. In total, 24 children between the ages of 5 and 16 years with ASD and severe behavior disorders were randomized to receive weekly intravenous injections of either placebo or 1 of the 2 interventions (glutathione or Trio) for 8 weeks. After a 1-week washout period, participants were crossed over for the subsequent 8 weeks. Behavioral measures and plasma levels of glutathione were obtained at baseline, during the washout period, and at the end of the study. RESULTS: No differences between treatment groups in behavioral or biologic measures were found. No significant adverse side effects attributable to the treatments were observed. Small improvements in specific glutathione and behavioral measures occurred over the study period for all groups. CONCLUSION: Treatment with glutathione or glutathione in combination with vitamin C and N-acetylcysteine did not result in improvements in behavior or biologic measures. The positive trends over the course of the study were likely due to the placebo effect or decreased anxiety associated with the study routine.