Caries detection at non-cavitated occlusal sites remains challenging. The present investigation deals with the suitability of four methods to detect dentine caries when fissure discolouration occurs: (1) visual inspection with magnifying glasses using modified Ekstrand criteria, (2) laser fluorescence measurement with KaVo DIAGNOdent device, (3) electric conductive measurement with ECM III, (4) electric conductive measurement with Cariometer CRM 800 (Gente, M., 1999, unpublished). A total of 550 sites were examined in vivo. To attain a gold standard, a minimal-invasive opening of this site was performed, if two or more methods indicated dentine caries. Lesion depth was determined visually and dentine softening as an indicator for caries activity was assessed with a dental probe. This way validated data were collected at 108 sites that were opened in the fissures of 60 teeth from 37 patients aged 6 to 16 and 17 to 30 years. ECM showed the highest performance in younger patients followed by Cariometer, DIAGNOdent and visual inspection (sensitivity/specificity/AUC 0.97/0.91/0.97, 0.82/0.82/0.93, 0.67/0.85/0.78 and 0.82/0.48/0.65). Compared with all dentine lesions, the detection of soft dentine lesions was less accurate for ECM and Cariometer (AUC 0.88, 0.82, 0.78 and 0.62). For older patients (17 - 30 years) the diagnostic performance of all methods decreased considerably (AUC 0.66, 0.53, 0.56 and 0.51). In conclusion, among the four methods used, ECM demonstrated the best suitability for dentine caries detection at non-cavitated, discoloured occlusal sites. The small and convenient Cariometer also proved to be a usable tool. Keywords: dental caries, dental fissures, diagnosis, diagnostic techniques and procedures