A sensitivity study of stochastic crustal and Moho models on Moho refracted first arrivals is presented. The crustal model is a self-affine velocity structure superposed on a linear velocity gradient. The Moho is represented by a first-order discontinuity with a topography which is also self-affine. The sensitivity of both travel-time and wave-field is considered. We found that the full wave-field around the Pn arrival is sensitive to crustal structures down to 1 km, and to Moho undulations down to 5 km. However, the first arrivals are only sensitive to crustal structure down to about 3 km, and to Moho structure down to 10 km. Our analysis suggests that the wide-angle full wave-field has a sensitivity that is intermediate between the sensitivity of the vertically reflected wave-field and wide-angle arrival times. These findings give some justification to the mainstream ray tracing approach to wide-angle data inversion, where resulting models incorporate only a moderate number of features at relatively large scales. ¿ 1999 American Geophysical Union