Using the surface-force apparatus, we have made Johnson-Kendall-Roberts (JKR)-type adhesion measurements between Langmuir-Blodgett (LB) bilayers of a novel glycine amphiphile. The bilayers show a pronounced adhesion hysteresis at low pH that is completely removed at high pH. The adhesion hysteresis is marked by a spatially varying adhesion gradient on unloading that can be explained in terms of pH-dependent jump-to-contact forces. In addition to providing some insight into the mechanisms of interfacial bonding in biological systems, the JKR technique applied to LB bilayers of peptide amphiphiles emerges as a novel, quantitative method for fundamental bioadhesion measurements.