FLIX is a radically new concept for the ultimate-stage chemical isotopic labeling of high added-value molecules (drugs, biologics, smart materials) with stable isotopes. It utilizes the unique properties of new generations of catalysts, which specifically and selectively exchange predetermined atoms and chemical motifs of end-use organic compounds. The ultimate outcome of the project is to devise and build a modular and adaptable flow chemistry system for the straightforward and combinable isotopic labeling of complex chemicals and biologics. The ‘FLIX machinery’ will use a combination of specialized reactor modules operating under continuous flow conditions, either in closed-loop or open systems for the on-line H/D, C-12/C-13, N-14/N-15 and methoxy group direct isotopic exchanges with an unprecedented efficacy and without any chemical alteration of the molecules. The project’s objectives are to: 1) develop new generations of organometallic catalysts for isotopic exchange reactions; 2) screen catalysts for the isotopic exchange on a relevant portfolio of organic molecules in batch and flow chemistries and assess catalyst robustness; 3) devise and validate the ‘combinable isotope labeling’ concept; 4) design and build an adaptable multi-module machinery for combinable chemical exchange labeling. FLIX synergistically associates the expertise and innovation potential of a mixed academic/industrial multidisciplinary consortium. The project is expected to have a multi-billion Euro positive impact on all sectors using stable isotopes in particular: 1) drug innovation, by accelerating preclinical studies, de-risking clinical trials and fostering the development of novel deuterated ‘heavy drugs’; 2) design of new tracers for diagnostic imaging with improved biological properties; 3) streamlining the production of multi-labeled complex molecules for NMR studies; 4) the development of novel isotopically-enriched materials.