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The purpose of this study was to test some effects of preheating NaOCl solutions using a commercially available syringe heating device. Irrigating solution temperatures in 10-ml syringes were measured. Stability of 5.25, 2.62, and 1% NaOCl solutions for 60 min at 20, 45, and 60°C was assessed using iodine/thiosulfate titration. Human pulp tissue dissolution capacity of a 1% NaOCl solution was gauged at the latter temperatures, and compared to corresponding values with a 5.25% solution at 20°C. Killing efficacy of diluted NaOCl solutions against 48-h incubations of Enterococcus feacalis ATCC 29212 was compared at 45°C and 20°C. Using the heating device, a 20°C solution reached 45°C and 60°C in 7 and 20 min, respectively. Solutions remained stable during the observation period. The 1% NaOCl solution at 45°C dissolved pulp tissues as effectively as the 5.25% solution at 20°C, while the 60°C/1% solution was significantly more effective (p < 0.05). A 100-fold increase in killing efficacy was observed between corresponding NaOCl solutions at 20°C and 45°C.