The purpose of this study was to compare the efficiency of endodontic retreatment using either rotary ProFile GTTM .06 tapered instruments or hand files of canals filled with GTTM obturators or laterally condensed gutta percha (GP). Forty-eight extracted single-rooted teeth having <20° curvature were divided evenly into four groups. After access openings were prepared, canals were instrumented using rotary nickel titanium ProSystem GTTM series 20 files .10, .08, .06 and .04 tapers, finishing with the .06 tapered file 0.5 mm from the apical foramen. A size #10 file was used to ensure apical patency before obturation. ThermasealTM Plus with either GTTM obturators or laterally condensed GP using a formed cone technique. After obturation teeth were stored at 37ºC in 100% humidity for 6 weeks. One tooth was removed from the study due a cracked root. Retreatment was performed using either .06 tapered Profile GTTM rotary instruments with chloroform, or hand files ISO sizes #15,20 and size 20 .06 tapered Profile GTTM with chloroform. Chloroform volumes were recorded and ranged between 20 and 100 µl. The time for retreatment was recorded when files reached working length and a size #10 file was able to pass through the apical foramen. A two-way ANOVA was used to examine obturation material and method of retreatment. Results indicated that retreatment technique, rotary (59 sec) versus hand instrumentation (230 sec), was a significant factor (p=.0001) compared to obturation material, laterally condensed GP (159 sec) versus GTTM obturators (127 sec), (p=.12), and to the interaction of retreatment technique and obturation material (p=.36). We conclude that rotary instrumentation is more efficient for endodontic retreatment than hand instrumentation for canals having less than 20 degree curvature.