OBJECTIVE: Bronchiolitis obliterans syndrome is the major cause of long-term graft failure in lung transplant recipients and may be partially reversible if diagnosed early and treated. Diagnosis is difficult because findings of transbronchial biopsy are often negative in patients with early disease. We are investigating a novel MR ventilation agent, hyperpolarized 3He, for evaluating ventilatory abnormalities in lung transplant recipients with suspected bronchiolitis obliterans syndrome. CONCLUSION: In this preliminary study, the extent of ventilatory defects revealed on 3He-enhanced MR images correlated with severity of bronchiolitis obliterans syndrome using an established clinical grading system. This new technique may hold potential for diagnosing bronchiolitis obliterans syndrome in lung transplant recipients.