US chemists have come up with a simple one-step trick to allow them to add radioactive hydrogen, tritium atoms, to a specific site in an organic compound for radiolabeling purposes. The trick was discovered almost by accident when the team noticed systematic changes in their NMR spectra that faded with time. The process could be used to track metabolic pathways taken by a pharmaceutical or other compound, a toxin, for instance. Earlier methods could incorporate tritium atoms in a molecule only adjacent to a directing group. Princeton University's Paul Chirik and colleagues were able to readily access other positions in their molecules.