This contribution presents the possibility of application of natural sorbent (Transcarpathian clinoptylolite (KL)) for immobilization of selected heavy metals in the sewage sludge. The influence of ion-exchange parameters (e.g. time, amount of zeolite) were discussed. Process of immobilization was performed using a static method (Batch). It was found that best possible conditions for immobilization of heavy metal ions were as follows: zeolite fraction 0.7-1.0 mm, 5 h of shaking, zeolite/sewage sludge ratio 2/98. (C) 2007 Elsevier Ltd. All rights reserved.