Strain in polyetherurea thermoplastic elastomers with poly(tetramethylene oxide) soft blocks and well-defined bisurea hard blocks was probed through changes in fluorescence resonance energy transfer between both covalently linked and randomly dispersed donor and acceptor probe molecules. The covalently linked fluorophores are shown to have superior strain sensitivity, while the dispersed probes give information on the affinity of deformation at the nanometer length scale. The method is proposed to be generally applicable to study deformation of elastomers at the molecular scale.