The evaluation of the bactericidal effect of different silver-containing materials where silver is available as Ag(+) (silver nitrate and different silver-exchanged zeolites), as metallic Ag(0) (commercial silver nanoparticles) or as oxide (silver (I) oxide) was carried out in order to elucidate the importance of the bioavailability of silver (i.e., as free ions, metallic particles, combination of them, clusters, complexes, partially soluble or insoluble salts, etc.) on its bactericidal action. For the different materials tested, their bactericidal effect is ordered in the following sequence: AgNO(3) > Ag-ZSM-5 > Ag(2)O > commercial silver-exchanged zeolite (granular) > commercial silver-exchanged zeolite (pellets) > Ag nanoparticles. In general, as the content of bioavailable ionic silver increases, the biocidal effectiveness of the corresponding silver-releasing material increases too. (C) 2011 Elsevier Ltd. All rights reserved.