Tritium-labelled fluoroazomycin arabinoside, [H-3]-FAZA, is a useful probe for the investigation of hypoxia, furthermore it is safer and easier to handle than the PET tracer [F-18]-FAZA when used in cell based assays. The only known synthesis of deuterium- and tritium-labelled FAZA was re-investigated and optimized. Then, a new and improved synthesis of [H-2]-FAZA was developed as a model process for tritium radiolabelling. This novel synthesis is expected to greatly facilitate access to [H-3]-FAZA. (C) 2013 Elsevier B.V. All rights reserved.