Experiments of wave transmission across a joint were carried out to investigate the visco-elastic response of the joint. Two models for wave transmission were examined with the experimental data. The results show that the velocity discontinuity model which includes the effect of viscosity is in better agreement with the experimental observations for both P- and S-waves under dry conditions than the displacement discontinuity model. This suggests that at the real asperity contacts, the solid material behaves visco-elastically to transmission waves in the high frequency range. A possible mechanism for the visco-elastic behavior is plastic flow at the asperities caused by high local pressure. ¿ American Geophysical Union 1993