The decrease in nitrification during succession was investigated in the Piedmont of Maryland. Stands of vegetation identified as early, mid, and late successional stages were monitored for available nitrogen and nitrifying bacteria throughout the growing season. Potential rates of nitrification in soils from the three stands were examined by laboratory incubations. Limitation of nitrification by lack of soil nutrients or by allelochemicals released by late successional species were evaluated. Soils from the early successional stand had higher N03- and lower NH4+pools than soils of the late successional stand. Both forms of available nitrogen were low in the mid-successional stand. Numbers of nitrifying bacteria decreased with successional age. Laboratory soil incubations corroborated the field data. A hypothesis of allelochemical inhibition of nitrification was not supported by laboratory soil incubations. No nutrient limitation to nitrification was apparent. Soil pH appeared related to decreased nitrification potential.