For approximately 20 years, there has been a concerted effort, by several different research groups, to simulate observed rainfall-runoff events from the well-known R-5 catchment, located near Chickasha, Oklahoma. These prior simulation efforts, with relatively simple models of Horton-type overland flow, have not been entirely successful, as the streamflow generation process for the R-5 catchment, as now recognized, may not be totally dominated by the Horton mechanism. In the effort reported here, a new fully coupled comprehensive physics-based hydrologic-response model, the Integrated Hydrology Model (InHM), is tested for two R-5 rainfall-runoff events. The InHM simulations in this study clearly show, in a hypothesis-testing mode, that both the Horton and Dunne overland flow mechanisms can be important streamflow generation processes for R-5 events. The InHM simulations reported here also suggest that accurate accounting of soil water storage can be as important as exhaustive characterization of spatial variations in near-surface permeability. ¿ 2001 American Geophysical Union