Chernozem soil was preincubated with 0.1% glucose, glucose plus ammonium nitrate, hydrolyzed casein or amino acids for five days and with 1% wheat straw, pectin, peptone or cellulose for ten days. The soil was modified by this treatment so that the pipecolic acid was oxidized in two steps, as was shown by two peaks on the graphic plot of the oxygen uptake. In the control soil sample preincubated with water, the oxygen consumption curve formed one peak. In brown soil it was necessary to increase the concentration of glucose and hydrolyzed casein to 1% to obtain the oxidation of pipecolic acid in two phasos. Approximately a third of the oxygen for the complete oxidation of pipecolic acid was consumed in the first phase of oxidation, another third in the second phase of oxidation. A relation was found between the occurrence of the second period of oxidation of pipecolic acid and the amount of organic carbon in the soil.