Abstract : This study was designed to examine the efficacies of the combination of EDTA and NaOCl, or ultrasonics with or without EDTA on smear layer removal from root canal. The effects of different working times of EDTA and NaOCl (1 or 2 min. for EDTA, and 0.5, 1 or 2 min. for NaOCl, i. e. six combinations) were evaluated in four segments in the canal : at orifice, middle third, and 3 mm or 1 mm from apical foramen (apical 3 mm or apical 1 mm, respectively). Combined irrigation of EDTA and NaOCl showed time-dependent effects. The treatment of 2-min. EDTA and 2-min. NaOCl was most effective in all combinations. However, its efficacy was somewhat lower at apical 3-1 mm, while the smear layer of the orifice to center was effectively removed. Ultrasonic irrigation without movement revealed that when it was used with water, only the smear layer in the segment contacted by the tip was removed, but partially, while using with EDTA it worked effectively throughout the whole canal. Taken together, totally ultrasonic irrigation with EDTA tended to be superior at the apical 3-1 mm to the combination of 2 min. EDTA and 2 min. NaOCl. Further studies of irrigation methods with syringes or ultrasonic irrigation time with EDTA and its concentration are needed.