Anaerobic culture media per se could degrade tetrachloromethane abiotically at 30 degrees C for 7 d. The degradation depended strongly on the concentration of vitamin B-12. On a molar basis, more tetrachloromethane was degraded than vitamin B-12, indicating that the degradation was a catalytic reaction, Tbe optimal degradation was observed when 1-2 mM sulfide, 0.5 mM ammonium, and 0.5-1 mM phosphate were supplied. Co2+ was also found to be important in degradation. Chloride ion and trichloromethane mere produced in the degradation, but dichloromethane, chloromethane, and methane were not.