Adverse reactions with DMSO-cryopreserved stem cell infusion are well-recognized. However, severe, life-threatening anaphylactic reactions with DMSO are very rarely described in the literature. We report here a 58-year-old female with AL amyloidosis who developed an unexpected episode of respiratory arrest a few seconds after the beginning of thawed stem cell product infusion. Fortunately, the patient was resuscitated successfully without the need for intubation. The prompt development of the reaction just a few seconds after the stem cell infusion convincingly implicates DMSO as the potential suspect. The presence of amyloid cardiomyopathy might have also contributed to this adverse event. Bone Marrow Transplantation (2000) 25, 1299-1301.