Background. Imaging photoplethysmography (IPPG) is a non-contact optical method for studying the blood supply to biological tissues. It is successfully used in various studies and diagnostic procedures as a tool for monitoring changes in local hemodynamics in response to various types of interventions or under any pathological conditions. In experimental biomedicine, urethane (Ur) and alpha-chloralose (Ch) have long been used to anesthetize laboratory animals, but according to the American Veterinary Medical Association, these drugs are not acceptable for euthanasia. Aim. To evaluate the latency period of cessation of cerebral circulation in rats anesthetized with a mixture of Ur-Ch after intravenous bolus injection of Ur-Ch at a lethal dose by means of the IPPG parameters: Amplitude of Pulsatile Component (APC) and Optical Intrinsic Signal (OIS), and to compare the results obtained with a similar indicator of fatal changes in systemic hemodynamics and gas exchange function. Methods. Studies were performed on 15 anesthetized, curarized Wistar stock rats, which were subject to routine euthanasia after completion of acute experiments. IPPG waveforms were recorded through thinned parietal bones, allowing visualization of intracranial vessels. Parameters APC, OIS, electrocardiogram (ECG), blood pressure (BP), CO₂ at the end of exhalation (EtCO2) and heart rate (HR) were recorded before, during and after infusion of a lethal dose (no less than 1000 mg/kg of Ur + 100 mg/kg of Ch); the duration of the infusion was 10-15 seconds. The main estimated magnitude was the time of extinction of life support functions (TELSF), determined from the moment of the start of Ur-Ch administration until the moment of death based on the achievement of a composite point consisting of three points, namely: cardiac arrest (HR is zero), a drop in mean BP below 10 mmHg, and a decrease in EtCO2 below 1%. Results. Bolus administration of Ur-Ch in a lethal dose to an anesthetized rat caused irreversible loss of life support functions already during the infusion, namely, cardiac arrest (TELSF=5.6 [4.0-7.0 sec]), critical drop in BP (TELSF=10.2 [8.2-11.7] sec), and cessation of gas exchange (TELSF=13.8 [12.9-15.5] sec). At the same time, characteristic changes in the patterns of IPPG signals were observed: cessation of APC (TELSF=5.5 [4.5-7.5] sec) and break of the OIS (TELSF=10.4 [8.3-12.3] sec), which indicate fatal disorders of the blood supply to the brain. Conclusion. Ur-Ch infusion at a dose of at least 1000+100 mg/kg appears to be a reliable and humane method of euthanasia of rats under general anesthesia. The use of IPPG made it possible to identify optical markers of cessation of cerebral circulation caused by Ur-Ch. Keywords: euthanasia, imaging photoplethysmography, urethane, alpha-chloralose.