The aim of this study was to compare the values measured with the Diagnodent®-system for caries detection to the caries extension in enamel. 40 filling-free human extracted teeth stored in physiological saline solution were examined. After cleaning the tooth the surface was examined with the Diagnodent®-system at three points (mesial, central and distal). After staining the sections with Toluidine Blue/Rhodamin B the caries extension of the areas measured with the laser fluorescence system could be examined by light microscopic analysis. With increasing extension of caries in enamel higher and more varying laser fluorescence values were measured (correlation coefficient: 0.85). The values of the laser fluorescence measurements (before embedding the teeth in light-activated plastic) could always be reproduced after 1.5 hours storing the teeth in physiological saline solution. Up to a measured value of 10 a caries in enamel of up to 0.3 mm depth can be expected. At the moment a classification of caries in enamel with the laser fluorescence system is not possible due to the strongly varying measured values. Keywords: caries detection, laser fluorescence, histology, Diagnodent-System