Comparative evaluation of the effect of ecologically hazardous pollutant, cadmium on Bdellovibrio-survival was followed on free-living and biofilm formatted on solid surfaces cells of predators. Results indicated that immobilized system are more stable due to renewal infection cycles. this has principal significance in development of the ecologically sound biotechnology for water decontamination using natural mechanism in the environment. (C) 2004 Elsevier Ltd. All rights reserved.