Several organophosphate-degrading bacteria were isolated from test turf green soil using clear zones formed around their colonies on plates supplemented with organophosphate isoxathion. The degrading activity of the isolates for isoxathion was tested by incubation in liquid cultures and evaluated by gas chromatography. Strain B-5 exhibited the highest isoxathion degrading ability in the isolates and it was identified as an Arthrobacter sp. A high concentration of nutrients in the media affected the isoxathion degrading activity of strain B-5. The bacterium could not utilize isoxathion as a sole source of carbon and phosphorus. The degradation products of isoxathion by B-5 washed cells were identified as its hydrolysis products, 3-hydroxy-5-phenylisoxazole and diethylthiophosphoric acid, suggesting that strain hydrolyzes the heterocycle ester bond in isoxathion. Arthrobacter sp. strain B-5 also hydrolyzed diazinon, parathion, EPN, fenitrothion, isofenphos, chlorpyrifos, and ethoprophos at rates dependent on the substrate. Of the organophosphorus insecticides examined, isofenphos was affected most by the hydrolytic activity of the bacterium, which completely removed the compound (10 mg/l) from cultures within l-h incubation.