The antibacterial effects of Cu2+-, Zn2+-, Ag+-, Ag-0- and cetylpridinium-exchanged montmorillonites were tested on Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213 strains which are highly resistant to antibiotics and cause severe infections in hospitalized patients. The exchange reactions were carried out using heavy metal and cetylpridinium (CP) cations in amounts that are equal to or less than the amounts required forming a monolayer on montmorillonite surface. The amounts required for the monolayer formation were determined by conducting batch adsorption experiments. The antibacterial activity of the samples was detected by the disk diffusion method. Cu2+-, Ag+-exchanged and Ag-0-covered montmorillonites had a good antibacterial effect against P. aeruginosa and S. aureus as did the Zn2+-exchanged montmorillonite against S. aureus. However, the CP-exchanged montmorillonite was ineffective for both of the bacterial species. Thus, the heavy metal exchanged montmorillonites could be used in pharmaceutical applications, personal care products, in the decontamination of P. aeruginosa reservoirs in hospitals, and also in aqueous based cleaning agents and liquid and bar soaps. Zn2+-exchanged montmorillonite has potentiality to be used as a low cost substitution to silver for applications against S. aureus. (C) 2010 Elsevier B.V. All rights reserved.