Two exopolyphosphatases (polyphosphatase I and II; EC 3.6.1.11) from Microlunatus phosphovorus isolated from an activated sludge, release orthophosphate from inorganic polyphosphates and have been detected and characterized for the first time, Polyphosphatase I has a molecular mass of 93 kDa, pH optimum of 4.5, does not require K+ for its activity and is stimulated by divalent cations. Polyphosphatase II has a molecular mass of 55 kDa. pH optimum of 7.5 and displays its optimal activity in the presence of K+ and divalent cations. The content of polyphosphatase I increases during growth, while polyphosphatase II varies only slightly. (C) 2002 Published by Elsevier Science Ltd.