This paper presents the changes in vegetation distribution and hydrological balance resulting from a change in soils input data to the biogeography model MAPSS (Neilson 1995). The model was run for the conterminous United States using three different sets of soil characteristics: (1) all soils were assumed to be sandy loam; (2) soil characteristics came from the Food and Agriculture Organization (FAO) soils map of the world (FAO 1974-1979) and (3) soil characteristics came from the Natural Resource Conservation Service (NRCS) National Soil Geographic (NATSGO) dataset. Resulting changes in vegetation distribution appear small on a countrywide basis, but large changes in simulated runoff in savannas, shrublands, and deserts reflect the importance of using the best available soils dataset. In the state of Oregon, a 16-percent relative decrease in forest areal extent is accompanied by an 18-percent relative increase in shrubland when switching from FAO to NATSGO datasets. Conversely, forest cover increases by 24 percent while shrubland extent decreases by 14 percent when all Oregon soils are assumed to be sandy loam. MAPSS vegetation distribution projections were compared to K�chler's potential vegetation map (K�chler 1964). The generalization of all U.S. soils to sandy loam soils decreases the similarity between MAPSS predictions and K�chler's map and is clearly inappropriate.