A proposed evaluation of the extent of interfacial debonding in binary blends is based on the comparison of tensile (or yield) strength with model predictions. The predictive scheme employs a two-parameter mechanically equivalent model and data on the phase continuity of constituents acquired from percolation theory. The upper and lower bounds of strength are related, respectively, to interfacial adhesion sufficient (A = 1) and insufficient (A = 0) for stress transmission between constituents. The values of A in the interval 0 < A < 1 are interpreted in terms of partial debonding of the fractions of constituents formally coupled in series.