To determine the difference of CBC values in different blood cell counters, we have measured the values of CBC by using reference cell counters of three major makers; Coulter, Sysmex and Technicon. Thirty ml of whole blood was taken from 2 healthy individuals and mixed with 45 mg of EDTA -2K. The blood samples were then sent to reference laboratory of each maker under identical conditions. The determination of cell counts was performed 4 hours after taking blood. Ten consecutive analysis were then carried out and the mean of 10 values was calculated. The apparent difference was displayed in leucocyte and platelet counts. In both of two samples, the highest values of either leucocyte or platelet count was obtained with Coulter instrument. And second high values were noted with Sysmex counter and the lowest values were observed by Technicon instrument. The extent of difference between each instrument was over 10% in case of platelet count and was 5 to 10% in leucocyte count. The difference of erythrocyte count, Hgb level, hematocrit value and MCV also existed, but the extent of difference was within 5% in all of these examinations. Since CV of each examination was sufficiently low level, this difference might be due to the difference in accuracy of reference cell counter of each maker. These results suggest that distinct differences of CBC count, particularly platelet and leucocyte count can be produced by the different procedures of calibration for reference counter in each maker of automated blood cell counter.