We have analysed the filling length in 495 teeth, the length of which was measured with various methods routinously used in practice today. Significantly better fillings of root canals after pulpectomy were observed in the group, in which the length of canals was measured with odontometer, in comparison with the group, in which the lengths were measured with the tactile sense method (P less than 0.01), and with the group, in which the length was measured with preoperative radiogram only (P less than 0.05). The odontometric method resulted in statistically significant reduction of overfilled teeth in comparison with the x-ray measurement and with the radiogram made with the instrument in the root canal (P less than 0.01).