Microcirculatory bed, as part of the whole human vascular system, is the link between blood, lymph, and interstitial space. Laser Doppler flowmetry (LDF) is traditionally used to study blood microcirculation. The aim of the study was to identify the wavelength ranges in which the differences in the reflection coefficient of vessels with different degrees of blood and lymph filling are maximal. The nature of the differences in the reflection coefficient may allow the estimation of the contribution of the blood and lymphatic components to the total reflected signal. Materials and Methods. The reflection coefficient on isolated blood and lymphatic vessels in the wavelength ranges commonly used in existing diagnostic systems has been investigated, the amplitude-frequency parameters of LDF signals characterizing the functional state of the blood and lymph flows have also been analyzed. The experiments were carried out on laboratory male Wistar rats. Static spectral characteristics of blood and lymph have been studied on isolated vessels obtained in the acute experiment using HR4000 spectrometer (Ocean Optics, USA). The portal vein and thoracic lymphatic duct of the living anesthetized rat have been selected as an object for studying LDF characteristics of the blood and lymph flow in vivo. Biopac LDF 100C diagnostic system (Biopac Instruments, USA) with a probe wavelength of 830±10 nm was used for measurements. Results. After the evacuation of blood or lymph in the isolated vessels, significant changes (p=0.0059) in the reflection coefficient in certain wave ranges (700–860 nm for lymphatic and 410–560 nm for blood vessels) have been registered that, in our opinion, allowed us to evaluate the dynamics of filling the probed object with blood or lymph, respectively. During heart contraction, a LDF signal with phase oscillations has been recorded on the thoracic lymphatic duct persisting after cardiac arrest. Its amplitude-frequency spectrum contained the predominant slow-wave harmonics increasing in cardioplegia. Conclusion. The results obtained demonstrate the possibility of the LDF method to record the signal characterizing the change in tissue perfusion due to the lymphatic flow. The spectral reflective properties of the isolated vessels are characterized by a multidirectional change in the reflection coefficient with a decrease in blood and lymph concentration in the studied tissue volume that should be taken into account when choosing a radiation source for LDF studies and developing new techniques of functional tests.