A lobe-plasma sheet boundary observed within Earth's distant magnetotail (XGSM≂-135 RE) with the Geotail spacecraft is interpreted in terms of a slow-mode shock. Measurements of the three-dimensional velocity distributions of protons and electrons and of the magnetic fields allow a quantitative comparison with theoretical predictions for a steady-state, one-dimensional shock. The observed plasma moments and magnetic field upstream from the shock are successfully used to predict these parameters in the downstream region. The measured parameters for this example of a lobe-plasma sheet boundary are in sufficient agreement with the theoretical predictions to provide considerable confidence that this boundary is a slow-mode shock. ¿ American Geophysical Union 1995