Introduction. With the advent of remineralizing therapies and the new, conservative approach to restoration placement, interest in detecting and monitoring subclinical, precavitated lesions has increased. The increased understanding of clinicians about the processes of primary and secondary prevention and the detection of lesions to which these therapies may be applied, is one of the current goals in caries management. Quantitative light-induced fluorescence (QLF) is a new method for the detection of very early caries. Objectives. To determine the ability of QLF to detect and longitudinally monitor in vitro enamel demineralization. To present the device to the paediatric community and present future in vivo uses of the device. Design. An in vitro study with combined in vivo pilot. Sample and methods. Twelve previously extracted, caries free, primary molars were selected and prepared. Two teeth were randomly selected as controls. Teeth were prepared by gentle pumicing and coating in an acid-resistant nail-varnish, except for an exposed window on the buccal surface. QLF baseline images were taken and the teeth then exposed to a demineralizing solution. Teeth were removed at regular intervals (24, 48, 72, 96, 120, and 144 h), air-dried and QLF images taken. QLF images were analysed by a single, blinded examiner (to control, to length of exposure). Mineral loss, as measured by ΔQ, was recorded. Results. Demineralization was noted in all experimental teeth by 48 h, and within 24 h in six teeth. The QLF successfully monitored the increase in mineral loss over time (P <0.05). The detected lesions were not visible clinically until 144 h and then in only the most severe lesions. No demineralization was detected by QLF in control teeth. The device was user- and patient-friendly in vivo, detecting subclinical lesions. Conclusion. Detection of very early mineral loss and subsequent monitoring of this loss is possible in primary teeth using QLF. The device is well suited to use in paediatric dentistry and offers applications for both clinicians and researchers. The determination of the status of carious lesions (active/inactive) will be possible with readings taken at recall appointments.