Several microbiologically produced biomolecules have been shown to degrade chlorinated contaminants found in groundwater systems. It was discovered that the cell-free exudates of the methanogen Methanosarcina thermophila were capable of carbon tetrachloride (CT) and chloroform (CF) degradation. Characterization of the exudates suggested that the active agents were porphorinogen-type molecules, possibly containing zinc. This research was performed to determine if the exudates from M. thermophila could be used for remediation purposes. The cell exudates were found to be capable of degrading CT, CF, tetrachloroethene, trichloroethene, and 1,1,1-trichloroethane. CT degradation was used to gauge exudate activity under a variety of conditions that would be encountered in the environment. The cell exudates were active when incubated in two types of soil matrices and at temperatures ranging from 4 to 23 degreesC. Over a 35-day period approximately 10.2 mu moles of CT were degraded by M. thermophila exudates. To test the hypothesis that the exudates contained either a zinc porphorinogen or a quinone, experiments were performed with zinc 5,10,15,20-tetra (4-pyridyl)-21 H, 23 H-porphine tetrakis, protoporphyrin IX zinc, and juglone. The two zinc porphyrins were capable of mediating CT degradation at rates comparable to those observed with the M. thermophila exudates; however, juglone was only capable of very slow CT transformation. The electron-transfer activity of the M. thermophila cell exudates was therefore more consistent with the activity of porphorinogens rather than quinones. Finally, in two enrichment cultures established from aquifer material and marine sediment, the possibility of excreted agents capable of degrading CT was evident.