The purpose of this study was to examine the effect of the use of EDTA as a root canal irrigant in curved root canals instrumented with nickel-titanium (Ni-Ti) instruments. Twenty extracted maxillary molars were selected. Mesiobuccal roots were used. Teeth were mounted in self-curing acrylic resin bases to allow standardized angulation of the initial and final radiographs. The preinstrumentation radiographs were made with a #15 file in the canal. The canals were instrumented with Ni-Ti instruments by the step-back technique, using or not using EDTA. The post-instrumentation radiographs were made with a #30 file in the canal. The films were projected (x10 magnification), drawn, and superimposed. Ni-Ti instruments used with EDTA were less effective in maintaining the original path of curved canals.