The biological activity of an ancient cultivated soil that has been in intense agricultural use since approximately the first half of the XVII century was studied. The potential biological activity of the buried horizon of the antient cultivated soil was higher than that of its modern horizon or that of the noncultivated soil of an adjacent territory occurring under similar lithological and geomorphological conditions. A decrease rate of oxidative processes (decreased rates of CO2 production and CH4 oxidation) and an increased rate of reductive processes (denitrification and nitrogen fixation) were found in the buried horizon. A high potential denitrification activity (with predominant formation of nitrous oxide) was found in the buried horizon; in the upper horizon, the end product was molecular nitrogen.