The internal N cycle in soils of native and established prairies is highly conservative of N, whereas that of cultivated soils has a greater potential for loss of N to denitrification and leaching. In addition to rapid plant uptake of inorganic N, the efficiency of the N cycle in prairie soils has been partly attributed to the quality and quantity of available C substrate to allow for microbial immobilization of N. In this study we investigate soluble or “free” anthrone-reactive carbon (ARC), as a measure of hexose sugars, soluble organic C, and soluble amino-N status of prairie and cultivated soils as possible measures of instantaneously available C and N.Soils were collected from 11 adjacent prairie and cultivated sites in July 1991. Field moist soil samples were analyzed for biomass C, KCl extractable NH4+, NO3−, and amino-N, and K2SO4-soluble organic C and ARC. Soil samples were also air-dried and analyzed for total C and N.Prairie soils were generally higher in total C, total N, biomass C, soluble amino-N, and soluble ARC than their cultivated counterparts. Total soluble organic C was not consistent among sites, but ratios of soluble C to inorganic N gave a better indication of the status of the internal N cycle than did the total C:N ratios.The prairie soils were lower in NO3−and total inorganic N than cultivated soils and had higher NH4+:NO3−ratios. This may reflect the tight internal N cycle in prairie soils. Net production of NO3−in systems where an available C source is limiting results in the accumulation of NO3−. Conditions of high NO3−and low levels of soluble ARC may be representative of a perturbed internal nitrogen cycle.