The aim of the present in vitro study was to determine the influence of different gutta-percha solvents used in endodontic retreatment cases on the accuracy of the Root ZX II electronic apex locator in locating the apical foramen. Thirty human, single-rooted permanent teeth were divided into three groups according to the solvent used: group OPO (orange peel oil, n = 10), group XYL (xylol, n = 10) and group CHL (chloroform, n = 10). Tooth length was established visually under 5× magnification with the aid of an optic microscope and then compared with the corresponding electronic measurement with a safety margin of ±0.5 mm. The results were analysed by the Biostat 4 program. The electronic and visual measurements coincided in 90% of the cases for xylol, in 100% of the cases for chloroform and in 100% of the cases for orange peel oil. No significant difference was observed among the three gutta-percha solvents in accurately locating the apical foramen (P = 0.607). Based on the results, it was possible to conclude that the accuracy of Root ZX II was not adversely affected by the presence of the gutta-percha solvents used in endodontic retreatment cases. Schlagwörter: electronic apex locator, tooth length determination, working length