The only effective method of obtaining leukoreduced blood components is filtration. Literature on leukoreduction reports that implementation of leukocyte reduction in blood components minimizes the risk of transmission of bacterial or viral infections, non-hemolytic febrile reactions, alloimmunization with HLA antigens as well as platelet transfusion refractoriness. In the Polish Blood Transfusion Centers leukoreduction has been used for many years now for the preparation of blood components dedicated to patients who can be administered only leukoreduced blood components. Standards set for residual leukocyte count ( a component to be marked as leukoreduced) are different for Europe and the United States. European standards set the residual leukocyte count below 1 × 106 leukocytes per unit of blood component. The criterium is also obligatory in Poland. European recommendations for leukoreduction require the implementation of effective and reliable methods of quality control. Much attention has lately been paid to the ADAM r-WBC system (Advanced Detection Accurate Measurement, Nano Entek, Seul, South Korea) based on counting WBCs in leukoreduced red blood cell concentrates (RBCCs) and leukoreduced platelet concentrates (PCs). The method was developed as an alternative to the hitherto used methods of residual leukocyte measurements in leukodepleted blood components. The aim of the study was to compare the leukocyte count measurements in leukoreduced RBCCs and leukoreduced PCs performed with 3 methods: microscopic, flow cytometry and automatic with ADAM r-WBC system. The study was conducted in two centers; the Institute of Hematology and Transfusion Medicine (IHTM — stage I) and in the Regional Blood Transfusion Center in Katowice (RBTC — stage II, following manufacturer’s verification and repeated validation). In stage I we used 94 samples of leukoreduced PCs and 34 samples of RBCC while in stage II — 29 samples of PCs and 26 samples of RBCC. The results of study stage I revealed that the residual leukocyte count measured with ADAM r-WBC system was much higher than the measurement with the microscopic method. Despite the higher values obtained in study stage I, the ADAM r-WBC system is in routine use for the measurement of residual leukocyte count in leukoreduced blood components at RBTC in Katowice as the system/ /equipment was verified and re-validated by the manufacturer according to the recommendations of IHTM and RBTC in Katowice.