Indiana University-Purdue University Indianapolis (IUPUI) / Introduction: Microbial biofilms have been shown to be a cause of persistent endodontic infections. It is more resistant than planktonic bacteria to host immune defenses and antimicrobials. Studies indicate that photodynamic light therapy (PDT), which involves using light at specific wavelengths, has a potent antibacterial effect on bacterial biofilm. PDT is an antimicrobial strategy that involves the use of a nontoxic photosensitizer (PS) along with a light source. The excited PS reacts with molecular oxygen to produce highly reactive oxygen species, which induce injury or death to microorganisms. PSs have a high degree of selectivity for inhibiting microorganisms without negatively affecting host mammalian cells. PDT has been suggested as an adjuvant to conventional endodontic treatment. Studies at IUSD have shown that blue light at 380 nm to 440 nm has the ability to inactivate Streptococcus mutans biofilm without any exogenous PS. Objective: The objective of this study was to determine the effectiveness of blue light at 380 nm to 440 nm to reduce adherence of Enterococcus faecalis biofilm after NaOCl irrigation at various concentrations. Materials and Methods: E. faecalis biofilm was established for 72 hours in 96- well flat-bottom microtiter plates using Tryptic Soy Broth supplemented with 1.0-percent sucrose (TSBS). Biofilm was irradiated with blue light for 5 minutes before exposure to various concentrations of NaOCl for 30 seconds. A crystal violet biofilm assay was used to determine relative density of the biofilm. Data were analyzed with two-way ANOVA and Sidak-adjusted multiple comparisons using a 5.0-percent significance level. Null Hypothesis: Blue light and NaOCl will not have an effect against E. faecalis biofilm adherence. Results: Overall, there was a significant effect (p < 0.05) for NaOCl and a significant effect for blue light. The effects of the combination of NaOCl and blue light were also significant. Conclusion: We reject the null hypothesis and accept the alternative hypothesis that blue light when used in conjunction with NaOCl will reduce adherence of E. faecalis biofilm.