Aim of this in-vitro study was to assess the intra- and inter-examiner repeatability of electrical resistance measurements of occlusal surfaces. This study comprised 117 carefully cleaned molars with sound and/or non-cavitated occlusal surfaces. All specimen were investigated independently by four dentists using the ECM device (Lode Diagnostics, The Netherlands) and six dentists using the Cariometer CRM 800. All dentists were familiar with the mode of function of these devices. The measurements were carried out site-specific without using contact gel. After an interval of one week, the same dentists reproduced the readings for assessing the intra-examiner repeatability. Inter- and intra-examiner repeatability were calculated using Lin's intra-class correlation coefficient (ICCLin), scattergrams and residual plots by Bland and Altman (1990). The ICCLin for the ECM device revealed a higher intra-examiner repeatability of 0.69 in comparison to 0.59 for CRM 800. The mean ICCLin for the intra-examiner reproducibility was 0.62 (ECM) and 0.67 (CRM 800), but the variability of inter-examiner readings was greater for CRM 800 (ICCLin 0.37 - 0.83) than for ECM (ICCLin 0.64 - 0.75).The limits of agreement (confidence interval of 95 %) showed for the intra-examiner repeatability (ECM) a deviation of -72.2/+62.2; the values for the inter-examiner repeatability amounted to -65.9/+62.4. The interval of limits of agreement were estimated for the CRM 800 between -4.4/+2.8 (Intra) and -1.9/+4.9 (Inter), respectively. Based on this in-vitro investigation it can be concluded, that the repeatability of both devices showed markedly deviations. The clinical use of these instruments can be only recommended in combination with other diagnostic methods. Keywords: Kariesdiagnostik, Elektrische Widerstandsmessung, Reproduzierbarkeit