The single filament pull-out test is used to directly examine fiber-matrix interface bond strength. The experimental results exhibit a dual behavior in pull-out load as a function of initial embedded length. With increasing embedded length the pull-out load rises, then appears to reach an asymptote. This behavior can be explained by a fracture mechanics argument. In addition, the large experimental scatter is proposed to be inherent in the small test specimen and to be caused by imhomogeneity in surface energy of the smooth fibers tested.