This pilot phase II study will follow a randomized, double-blind, placebo controlled, parallel group design. Consenting subjects who have undergone hematopoietic stem cell transplantation at the NIH Clinical Center will be randomized 50/50 to receive dexamethasone 0.01% solution or placebo as an oral rinse for 3 months starting 90-100 days post-transplant. Subjects will be evaluated monthly after the start of intervention. Diagnostic and research evaluations will include a complete oral examination, oral mucosal biopsy prior to the beginning of the intervention (day -7) and at the time of development of oral chronic GVHD or at the completion of intervention in the absence of clinical GVHD. We will measure serum dexamethasone levels and perform short cosyntropin (ACTH stimulation) test at the end of the 3-months of intervention or onset of clinically significant GVHD.