OBJECTIVE To compare the antibacterial effect of the passive ultrasonic to passive sonic irrigation with a 5.25% NaOCI solution. METHODS Sixty human teeth were used. The crowns were removed and the roots were instrumented prior to sterilization and incubation with Enterococcus faecalis. Five mL of 5.25% NaOCI were used during a 3 min final rinsing with: syringe irrigation (n = 20), passive ultrasonic irrigation with the Irrisafe (n = 20) and passive sonic irrigation with the Endo Activator (n = 20). A sterile file was used to remove dentine shavings at the apex and placed in BHI. After 72 h, this infusion was used to inoculate blood agar plates. The presence or absence of Enterococcus faecalis colonies was determined and statistically analyzed. RESULTS No statistically significant difference was found among the 3 groups. None of the irrigation regimen permitted to obtain 100% of bacteria free teeth. CONCLUSIONS The passive agitation of the irrigation solution did not increase its antibacterial efficiency. Longer irrigation times may be required.