The relationship between the Tate at which cracks heal and the stress field surrounding the crack tip has previously been suggested as a way to characterize the adhesive properties of viscoelastic systems. Crucial to this description of adhesion is a predicted unique relationship between the crack healing velocity and a stress intensity factor which completely characterizes the stress field; it has been shown that this relationship should be independent of the applied loading history. We have experimentally investigated this characterization of adhesion using JKR-type contact mechanics methods. The experimental results indicate a dependence on the loading rate in the relationship between the crack healing velocity and the stress intensity factor, contrary to the predictions of the theory. It is suggested that this may be due to nonlinear material behavior near the crack tip, as the theory is based on linear viscoelasticity. More ideal systems may produce better agreement between theory and experiment.