A multidisciplinary approach involving chemistry, microbiology, ecotoxicology and environmental engineering was undertaken by the Defence Research Establishment of the Department of National Defence (DREV/DND) and the Biotechnology Research Institute of the National Research Council of Canada (BRI/NRC) to characterize and to optimize the biodegradation potential of TNT and RDX in pure form and in soil. The nature and level of contamination by RDX and TNT in various soils were determined in an interlaboratory study involving both organizations using EPA Method # 8330. Microorganisms were isolated from the native soils and found to be capable of mineralizing (14CO2 liberation) RDX under aerobic conditions when the latter was used as sole nitrogen source. RDX disappearance was accompanied by the elimination of toxicity associated with RDX, as determined by the Microtox test. Studies are underway to use the isolated indigenous strain as a bioaugmentation agent for future site application. Thus far TNT showed more toxic effects than RDX and metabolic analysis showed that TNT was biotransformed into the more toxic amine metabolites. In soil these amine metabolites react with humic acids to give recalcitrant and intractable products. To eliminate problems associated with TNT mineralization in soil we thus undertook a study to first wash TNT out of the soil using several water additives and then treat the TNT washings. Preliminary data showed that mineralization of TNT using sewage sludge under both aerobic and anaerobic conditions was enhanced in the presence of cyclodextrins. Further enhancement in the mineralization rate of TNT was obtained after subjecting the soil extract to photolysis. In an integral study, soil heavily contaminated with RDX (2000 ppm) and TNT (1000 ppm) was treated in bioslurry reactors supplemented with sewage sludge under both aerobic and anaerobic conditions. The biological performance of these reactors was monitored using microcosms spiked with 14C-labelled TNT or RDX. Preliminary data showed that RDX was almost completely mineralized. TNT rapidly disappeared (biotransformation to amino derivatives) with little mineralization. The data obtained from the present aerobic, soil washing and bioslurry reactors studies will be used for the development of practical soil remediation technologies.