The ability of two instrumentation techniques to negotiate and enlarge small curved canals was com-compared radiographically. Fifty canals in extracted human molar teeth were instrumented by the progressive enlargement (PE) technique, a form of step-back preparation using standard K files, or by the balanced force (BF) technique using K files whose tips had been specially modified. By using drawings and projected radiographic images of the files, the position of the largest file used in the apical preparation, #30 or #35 for the PE technique and #45 for the BF technique, was compared with the position of a small file placed in the canal before instrumentation. The PE and BF techniques were equally capable of instrumenting small curved canals to their respective largest apical preparation sizes. However, at sizes equivalent to the largest apical preparation sizes used in the PE technique, the BF technique produced significantly less deviation from the center of the original canal.