A procedure was developed to subdivide a drainage area into units that respond similarly. These were defined hydrologic response units and were a funtion of soil texture, soil depth, land use, and hydrology group classification. A computer model was developed to generate excess precipitation for each hydrologic response unit based on the Mein and Larson and Holtan infiltration equations. Data for several major storms from a natural watershed, located in Virginia, was used to evaluate the technique. The results showed significant variability between response units reaffirming the need to consider the vegetative-soil characteristics separately. Sensitivity analyses were made to evaluate variations in soil texture, depth of A horizon, soil hydrology group classification, and land use relative to excess precipitation estimates. Interactions were not studied. Advantages of this system compared to a lumped-parameter model were discussed. The most important advantage, particularly for the planner, is that spatial uniqueness is maintained for all response units. / M.S.