Variations in patterns of ammonification and nitrification among and within four sites at each of three stages of old field succession (old field to pine to deciduous hardwoods) were evaluated by laboratory incubations in May and August 1979. Each experiment included mineral nutrient-minus-nitrogen (-N) and supplemental ammonium (+ N) treatments to examine limitations on nitrification. In general, nitrate production was highest and ammonium accumulation was lowest in old field soils compared to pine or hardwood soils. However, there was considerable overlap in response, and variation due to locality within site and site within successional stage exceeded that attributable to successional stage alone. Ammonium addition enhanced nitrification in soil from all old field sites, only one pine forest site and no hardwood site. Addition of nutrients less nitrogen (-N) had no effect in any soil. Correlations between other soil variables and changes in ammonium and nitrate during incubation varied among successional stage and in some instances between dates. © 1985.