Data from volcanic ash-influenced soils indicates that soil pH may change by as much as 3 units during a year. The effects of these changes on soil chemical properties are not well understood. Our study examined soil chemical changes after artificially altering soil pH of ash-influenced soils in a laboratory. Soil from the surface (0-5 cm) and subsurface (10-15 cm) mineral horizons were collected from two National Forests in northern Idaho. Soil collections were made from two undisturbed forest stands, a partial cut, a natural bracken fern (Pteridium aquilinum [L.] Kuhn) glade, an approximately 30-yearold clearcut invaded with bracken fern, and a 21-year-old clearcut invaded with western coneflower (Rudbeckia occidentalis Nutt.). Either elemental sulfur (S) or calcium hydroxide (Ca(OH)2) were added to the soil to manipulate pH. After 90 days of incubation, pH ranged from 3.6 to 6.1 for both National Forests and all stand conditions. Total C, total N, and extractable base cations (Ca, Mg, and K) were generally unaffected by pH change. Available P increased as pH dropped below 4.5 for both depths and all soil types. Nitrate was highest at pH values greater than 5.0 and decreased as pH decreased indicating that nitrification is inhibited at lower pH. Contrary to nitrate, potentially mineralizable N increased as pH declined. Total acidity and exchangeable aluminum increased exponentially as pH decreased, especially in the uncut and partial cut stands. Data from this laboratory study provides information on the role of pH in determining the availability of nutrients in ash-cap soils.