Allogeneic haematopoietic stem cell transplantation (HSCT) has been widely used for the treatment of haematological malignant and non-malignant haematologic diseases. However, acute graft-versus-host disease (aGVHD) is a kind of severe complication of HSCT limiting its application. Cytokines such as tumour necrosis factor-α (TNF-α), IL-6 play an extremely important role in the formation and development of aGVHD. Besides, the oxidation phenomena and/or the formation of free radicals have been suggested to be causally related to various haematological disorders including aGVHD. Reactive oxygen species (ROS), such as hydroxyl radicals, play an important role in the formation and development of aGVHD. Hydrogen has been reported to have the ability to inhibit levels of cytokines such as TNF, IL-6 in vivo. Our recent studies provided evidence that hydrogen inhalation can selectively reduce cytotoxic oxygen radicals and exert antioxidant effects. Therefore, we suggested that hydrogen may have therapeutic effects on aGVHD. This hypothesis entails many experimentally testable predictions. We propose the experimental study by detecting complete blood counts (CBC) and Clinic signs of aGVHD mice. We also propose to detect the levels of TNF-α, IL-2, IL-1β, IL-6 which play important roles in the pathogenesis of aGVHD. To discover potential mechanisms of the therapeutic effects of hydrogen on the aGVHD model, we will examine gene-expression profiles. This study will open a new therapeutic avenue combining the field of therapeutic medical gases and aGVHD. This theory is original and probably of importance, because therapeutic medical gases have never been used for aGVHD previously.