The in vitro antibacterial activity of the glass-ionomer restorative cements Ketac-Cem, Ketac-Bond, Ketac-Silver and Vitrebond was studied in conjunction with 32 strains of five bacteria involved in the development of caries: Streptococcus spp., Lactobacillus spp., Actinomyces spp., Porphyromonas spp. and Clostridium sop. The agar plate diffusion method was used for the cultures, which included a chlorhexidine positive control. All the glass-ionomer cements rested inhibited bacterial growth, but with considerable differences in the scope of their action. Of the four cements, Vitrebond, a resin-modified glass-ionomer cement, was determined to be the most effective bacterial inhibitor.