A system for monitoring the blood supply to a transplanted organ consists of a transmitting section ( V ) 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 ( P ) with receivers ( P 1 to P M ) with a photosensitive sensor ( D ), 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 ( DAC ) 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 ( P ), 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 ( D ), the output of which is connected via a current/voltage converter ( IlV ) and via an analog band-pass filter ( PP ) to the input of an analog-to-digital converter ( ADC ), 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 ( MP ) connected via the integrator ( I ) with resetting and via a sampling switch ( S ) 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 ( HP ) , the output of which is connected via a squarer circuit ( KV ) 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 ( K ), 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 ( PP ), 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 ( G ), 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 . <EOS>