Fluorescence of carious human teeth at different stages of the disease was investigated in vitro. Fluorescence was excited using different sources of laser radiation at the wavelengths of 405, 445, 532 and 660 nm. It was found that the intensity of fluorescence excited by violet and blue radiation from the areas of teeth moderately and severely affected by caries was significantly higher than that from the intact hard dental tissues. In contrast, it was much lower from the areas affected at the initial stage of caries. The areas with superficial or deep carious lesions were characterized by intense luminescence in the red spectral range and its intensity further increased with the progression of the disease. On the contrary, healthy teeth did not show luminescence bands in the longwave range. The intensity of fluorescence from the carious areas excited by green light was much higher in comparison with that from the healthy ones at all stages of caries disease. Under excitation with red light, the fluorescence signal was produced neither in the healthy areas of hard dental tissue nor in the areas of carious lesions. The obtained results testify to the possibility of applying a rather inexpensive system for the reliable early detection of the carious processes in clinical practice.