A technique is described for measuring the displacements in fibers due to loading the composite. Fiber access was obtained by removing only very small pieces of the matrix, thereby minimizing the change in residual stresses. Fiber stresses were obtained near a hole, a slit, and a fatigue crack. It was found that fibers slipped within the matrix at a stress of 2 to 2.6 GPa near both the hole and slit; after cyclic loading the specimen with a hole, fiber stress at slip increased to 2.6 to 3.6 GPa. Fiber stresses bridging the wake of a fatigue crack were found to be approximately constant. The models used to compute a stress intensity factor at the tip of a bridged fatigue crack are reviewed, and it is shown that those assuming a constant fiber stress gave the best results.