The biodegrading ability of drainage water from research laboratories to dichloromethane (DCM) and chloroform (CF) was surveyed. When DCM was used as a sole carbon source in a synthetic mineral salt medium, some water samples showed ability to degrade DCM, and DCM-degrading bacteria were isolated from them, whereas no samples showed CF degradation activity. Two isolates, strain P3310, a Flavimonas sp., and strain G31, a Chryseobacterium sp., were used for further investigations. Both strains were able to use DCM as a carbon source for growth and also grow in complex media containing other carbon sources, suggesting they were facultative methylotroph. Both strains needed 6 days at 30 degrees C to completely degrade 200 mg/l of DCM with the first isolated cells, but this was shortened to 2 days with the first subculture, suggesting they were acclimatized. Although the DCM-degrading activity of strain G31 was inhibited by addition of other carbon sources such as peptone or glucose, that of strain P3310 was not affected. Thus, strain P3310 may be a useful candidate for bioremediation to eliminate DCM from drainage.