The primary task in treating acute blood loss and resolving its complications consists in the correction of the decreased circulating blood volume by means of infusion and transfusion therapy This task can be achieved provided that the volume of the blood loss has been precisely evaluated. Aim. To propose a method for assessing the volume of intraoperative blood loss based on determining hemoglobin concentration in the washing medium by a hemichromic method. Results and discussion. The data obtained during approbation of the proposed method confirms its efficacy for assessing the volume of intraoperative blood loss. The hemichromic method for determining hemoglobin concentration is based on the reaction between the transforming solution and all three Hb forms (A, A2 and F), which leads to the transformation of HbA, HbA2 and HbF into an oxidized low-spin form (hemichrome HbChr). This form has the maximum light absorption at 540 nm, the intensity of which is directly proportional to the concentration of hemoglobin in the probe. Sodium dodecyl sulphate (SDS) was used as a reagent to transform Hb into HbChr. This reagent is low-toxic and safe in the applied concentrations; moreover, it requires no special conditions of storage, transportation and utilization. The optical density was estimated using a biochemical photometric kinetic analyser. The method was tested on 147 patients that underwent urological interventions. Conclusions. The precision and simplicity of the proposed method for assessing the volume of intraoperative blood loss based on measuring hemoglobin concentration in the washing medium by the hemichromic method make it suitable for application in clinical practice for endovideo-assisted surgical interventions in urology.