The effects of Nd:YAG laser irradiations at different power settings on several oral pathogens were evaluated. A total of 252 dentin samples were divided into seven groups consisting of 36 dentin specimens each. In each group, 9 of the 36 specimens were used as controls, thereby including a control in every group. The remaining 27 specimens were divided into three subgroups consisting of nine specimens according to different Nd:YAG laser settings (1.5, 1.8, and 2 W). Each group was inoculated on the nonpulpal side with one of the following microorganisms: Candida glabrata, Candida tropicalis, Candida krusei, Candida sake, Candida lusitaniae, Candida kefyr, and Rhodotorula mucilaginosa. The following irradiation procedure was used: the specimens were irradiated on the bacteria-free side (the side consisting of the pulpal wall) using contact mode under the constant scanning movement of the optical fiber at an angle of 10A degrees. One lasing cycle consisted of four irradiation cycles of 10 s each, with 15-s intervals in between each irradiation cycle. The remainder of the controls and the lased specimens of each group were prepared for the microbiological investigation. After incubation for 24 h at 37 A degrees C, the colonies were counted, and the total number of surviving microorganisms was statistically assessed. Microorganisms irradiated with Nd:YAG laser at power settings 2 W, 15 pps did not survive. Although there was a significant reduction of microorganisms at 1.5 and 1.8 W, when comparing Nd:YAG laser irradiation with the control group, sterilization did not occur.