A system for monitoring the blood supply to a transplanted organ consists of a transmitting section with transmitters ( V 1 to V N) with light-emitting diodes ( D 1 to D L), which irradiate the monitored tissue by radiation at various wavelengths, of a receiving section with receivers ( P 1 to P M) with a photosensitive sensor, which detects the radiation reflected from the monitored tissue, and of a control section ( μP), which generates excitation pulses ( u [ n]) for the transmitters ( V 1 to V N) and processes the signals from the receivers ( P 1 to P M), characterized by the fact that each of the transmitters ( V 1 to V N), which are N in total, where N corresponds to the number of wavelengths used for irradiation, comprises at its input a digital-to-analog converter connected to the input of a voltage/current converter ( V / I), the output of which is connected to at least one light-emitting diode D 1 to D L for the wavelength of the given transmitter ( V 1 to V N), and if multiple light-emitting diodes ( D 1 to D L) are used, they are connected in series between the output of the voltage/current converter ( V / I) and the power supply voltage (+ V cc), each of the receivers ( P 1 to P M) in the receiving section, which are M in total, where M is given by the requirement for the volume of the monitored organ or its part, is formed by the photosensitive sensor, the output of which is connected via a current/voltage converter ( IlV) and via an analog band-pass filter to the input of an analog-to-digital converter, while its output is the output of the given receiver, and each of the outputs of the receivers ( P 1 to PM) is connected to the first input of its respective demodulator ( DM 1 to DM M) in the control section ( μP), the demodulators ( DM 1 to DM M) comprise at their inputs the multiplier connected via the integrator with resetting and via a sampling switch to the input of their relevant switchers ( S 1 to S M), while each of them has N outputs and each of these outputs is connected to one feature estimator ( E i1 to E iN) for each wavelength, and each feature estimator ( E i1 to E iN) is formed by two parallel branches, where one branch is formed at its input by a high-pass filter, the output of which is connected via a squarer circuit to the input of the first low-pass filter ( DP 1), and the output of the first low-pass filter ( DP 1) is the output of the signal ( A y[n]) corresponding to the amplitude of pulsations of the radiation reflected at the given wavelength, and the second branch is formed at its input by the second low-pass filter ( DP 2) and its output is the output of the signal ( I y [ n]) corresponding to slow changes of the reflected radiation intensity, and the outputs of all feature estimators ( E i1 to E iN) are connected to a classifier, while the control section ( μP) further contains a digital filter ( H(z)) and its transfer function corresponds to the discretized transfer function of the analog band-pass filter, where the output of the digital filter ( H(z)) is connected to the second inputs of the demodulators ( DM 1 to DM M), and its input is connected to the output of the generator, which is simultaneously connected to the input of the common switcher ( S u), which has the outputs connected to the inputs of the individual transmitters ( V 1 to V N) so they can be sequentially activated during the elementary measuring interval T p by the pulse u [ n] with the sampling frequency f s according to the equation u n = w n ⋅ sin Ω 0 n + k, where w [ n] is the weight window with length N w samples, Ω 0 is the central normalized frequency of the pulse, and k > 1 is a constant, while for the total length of the pulse u [ n] holds that T p · f s > N w.