Abnormalities of immune surveillance may contribute to the development of myeloid malignancy as well as immune-mediated diseases. In leukaemia, allogeneic haemopoietic stem cell transplantation (alloHSCT) has been used to induce disease remission, in part by restoring mechanisms of immune regulation. Although, by the same principle, allogeneic stem cell transplantation is an attractive option for the treatment of immunological disorders, it is unclear whether remission after transplantation is due to pre-transplant conditioning, or modulation of auto-reactive lymphocytes by cells in the allograft. We report the case of a patient with chronic myeloid leukaemia (CML) who received an allogeneic bone marrow transplant (alloBMT) from his brother. He subsequently suffered a cytogenetic and molecular relapse of CML. At the same time, sarcoidosis involving the marrow was diagnosed. He was treated with donor lymphocyte infusions (DLI) and attained remission from CML; in addition, no giant cell granulomas were detected in the marrow, indicating resolution of sarcoidosis. This case illustrates the need for further studies on the role of T cell-based therapies in the management of immune-mediated disorders.