Two composting systems were compared on a laboratory scale as a bioremediation technology for degradation or immobilization of 2,4,6-trinitrotoluene (TNT) in contaminated soils. The first compost was aerated from the beginning whereas the second compost was only aerated after an anaerobic prephase of 65 days. In the first compost system the TNT concentration declined rapidly by 92% but, at the end, TNT could be partially recovered. During the anaerobic prephase of the second compost system, TNT was almost completely converted to aminodinitrotoluenes, which during the subsequent aeration almost entirely disappeared. In addition, the second compost generated less toxic material than the first one as confirmed by inhibition of bioluminescence of Vibrio fischeri. These data show that microbiological TNT-degradation systems can be successfully designed which are prerequisite for an efficient bioremediation of contaminated soils.