Three lining materials, Life, Ketac-Bond, and IRM, were investigared for their antibacterialeffects within dentinal tubules. Sterile saline served as control. Sixty standardized bovine root specimens were infected with Enteroccoccus faecalis following smear layer removal. The materials were mixed according to manufacturer's directions and inserted in the canal lumina; additional IRM specimens received a softer than normal mix. Specimens were incubated for 24 hours or 7 days, after which dentinal samples were taken from within the limina and the numbers of bacteria present were assessed. All the materials had a significant antibacterial effect after 7 days. Life demonstrated a more marked effect at 7 days than at 24 hours. The strongest antibacterial effect at 24 hours was shown by a soft mix of IRM. Ketac-Bond demonstrated an increase in antibacterial activity during the experimental period.