There are two major concerns about prescribed fire reintroduction into over-stocked ponderosa pine stands on the Mogollon Rim of Arizona. The first of these deals with the nitrogen status of soils that are already nitrogen limited. The second is over potential changes in soil carbon content that might further aggravate nutrient limitations and accelerate carbon release to the atmosphere. Prescribed fires were ignited at intervals of 1, 2, 4, 6, 8, and 10 years to determine the best fire return interval for reducing forest floor and over-story fuel loads ponderosa pine ecosystems. Two sites were treated; one on volcanic-derived soils, and the other on sedimentary-derived soils near Flagstaff, Arizona, starting in 1976 and 1977, respectively. Samples from upper 5 cm of the A horizons were analyzed for total carbon and nitrogen using a CNS analyzer. Soil carbon (3.0 – 5.6%) and nitrogen (0.20 – 0.35%) levels were highly variable, but exhibited a trend of increasing concentration related to burn interval. High spatial variability found within treatments was most likely due to micro-site differences (location of samples in the open, under large old-growth trees, in small-diameter thickets, in pole-sized stands, next to downed logs, etc.).