The authors evaluated the performance of four modern, commercially available hematology analyzers for imprecision and inaccuracy in determining the leukocyte differential count. The evaluation was performed according to International Committee for Standardization in Haematology protocols and the National Committee for Clinical Laboratory Standards H20-T standard, using the same group of patients simultaneously. Imprecision was very low among all the analyzers for neutrophils and lymphocytes (coefficient of variation maximum = 4.12%), whereas for the other leukocyte populations it tended to increase as their presence percentage decreased. The imprecision of the analyzers was still lower than that of the microscopic method. The correlation with the manual 800 cell count (inaccuracy) was good for neutrophils, lymphocytes, and eosinophils (r = 0.974 to 0.888), less so for monocytes (r = 0.757 to 0.490), whereas it was poor for basophils (r = 0.532 to 0.078).