Abstract IR-spectra of the samples of the dentine and gingival fluids obtained with the use of synchrotron radiation can be applied for the diagnostics of the pathological processes of the caries character in a dentine. Vibrations within the range of 2100-2050 cm⁻¹ observed in the spectra of dentine and gingival fluids characteristic of thiocyanates mean the development of the carious pathology. At the same time vibration modes of the carboxyl group of a complex ether detected within the range of 1765 – 1725 cm⁻¹ in the spectra of dentine and gingival fluids certainly confirm the development of caries in dentine. These spectrometric signatures can be certainly and reliably detected also in the gingival fluid, indicating at the fact that the changes proceeding in its molecular composition are referred just to the development of pathological processes in the deep dental tissues.