Pyrolysis in combination with gas chromatographic separation and simultaneous nitrogen-phosphorus and flame ionization detection is proposed for the determination of nitrogen compounds in soils. Peak identification was performed by mass spectrometry. The technique is considered as a complementary tool for use with other techniques for soil organic matter studies. The pyrolysis probe was placed directly in the horizontal injection port of a Perkin-Elmer Model 8700 chromatograph coupled with a nitrogen-selective detector and a flame ionization detector and into the vertical injection port of an HP-5890A chromatograph coupled with an HP-5989 mass spectrometer. This technique was applied to study the evolution of the organic matter in soils amended with sewage sludge samples.