This study investigates how storage temperatures and periods under extended idle conditions affected the stability and activity of granules that have a high phenol-degrading capability. The granule activity increased as storage temperature decreased, and declined as storage time increased. Granules stored with pure water at room temperature (20.8+/-5.6 degrees C) lost stability after three months storage. Particularly, granules stored with 500 mg l(-1) phenol solution demonstrated high phenol degradation capability following storage. Further, storage at subfreezing temperatures (-20 degrees C) is an ideal way of preserving stability and activity of phenol-fed granules. Anaerobic degradation of proteins in granule core by obligate anaerobic strain such as Bacteroides sp. corresponded to the stability loss of stored granules.