The aim of this study was to assess the reliability of linear meas-urements of interproximal bone loss on digitized radiographic images after the use of different filters. Immediately before surgery 50 radio-graphs of 50 teeth with inter-proximal intrabony defects of 50 patients were obtained. Intrasurgically the distances from the cementoenamel-junction (CEJ) to the alveolar crest (AC) and from the CEJ to the deepest extension of the bony defect (BD) were assessed. All radiographs were digitized. Using the FRIACOM-software, the linear distances CEJ-AC and CEJ-BD were measured at the defects on digitized but unchanged radiographic im-ages and after the use of 2 image processing modes (filters: "spreading", "structure") with 7x and 14x magnification by 2 examiners. Repeated measures MANOVA revealed reproducibility of the measurement of the distance CEJ-AC to be significantly influenced by examiner (p = 0.01), height of 2 wall component of the intra-bony defect (p