Patients after stem cell transplantation (SCT), often develop graft-versus-host disease (GVHD) which, although potentially dangerous, is associated with the beneficial graft-versus-leukemia (GVL) effect. Where there is high risk of disease recurrence, donor lymphocyte infusions (DLI) are given to provide long-term disease control. We present a patient treated with DLI 4 years post-SCT, who developed acute GVHD after administration of progesterone to induce menstruation. This rare allergic reaction warrants further investigation.