The authors describe the application of a high-resolution time-domain reflectometer (TDR) to detect debonds in Space Shuttle tile structures. Experimental measurements on bonded and debonded tiles are included to demonstrate the technique. The work utilized the high sensitivity and resolution possible with the Hypres PSP-1000 TDR system. Experimental measurements of TDR waveforms launched on the tile via a WR-28 rectangular waveguide horn with a lens showed that different signatures can be obtained from bonded and debonded regions. Computer simulations were used to verify the experimental results. The results obtained demonstrate the feasibility of using high-resolution TDR methods for detecting tile debonds. >