Summary.Anin‐vitroradiographic study of human teeth was performed in order to evaluate the ability of radiographs to determine the location of the apical foramen. The tip of an endodontic file was positioned at the apical foramen of each canal in 117 extracted human teeth (213 canals) and in 56 teeth (92 canals) still within the alveolus of dried jaw specimens. Parallel radiographs were taken in a bucco‐lingual plane of all teeth. The tip of the instrument appeared to be at the root surface (apical foramen) in 82 per cent of canals. There was no significant difference in results between the teeth radiographed in alveolus of dried jaw specimens and extracted teeth when the radiographs were evaluated under a stereomicrosc