A cut-back asphalt and an asphalt-in-water emulsion were tested for improving soil structure and controlling erosion of soil by wind. The materials applied as fine spray at rates up to 400 gallons per acre, on the basis of undiluted material, produced a film which initially was completely effective in holding various soils against wind. The finer the spray and the more dilute the solution or suspension, the more uniform and stable was the film. The film was effective only for about 2 weeks on clay soil and for at least 2 months on sand and loamy sand. The film was generally porous and took in rainwater readily. Germination and emergence of wheat, grass, and legume seeds were unaffected by the asphalt film. Asphalt mixed with soil produced a high degree of soil aggregation in both wet and dry state and decreased erodibility by wind, but only for about 2 years. After this period, the treated soil became progressively more granulated and more erodible by wind but continued to have a substantially greater proportion of water-stable aggregates and to be much more permeable by water. Changes in physical properties of asphaltic cement in soil and its relationship to soil structure and erodibility were recorded and explained. Cement added to soil, it was concluded, will be effective against wind erosion only so long as its sticky property is maintained.