The present study evaluates the performance of automated white blood cell (WBC) differential counts by the new Haematology Analyser SF-3000. Five hundred and sixty-six WBC differential counts performed by the SF-3000 were compared with WBC differential counts of the well established analyser NE-1500 and to manual reference counts. Numerical results of the WBC differential counts were correlated to each other by regression analyses. The efficiency of instrument flagging for the presence of abnormal WBC was expressed as per cent of subjects correctly classified. Neutrophil and lymphocyte counts correlated well between analysers and to manual reference counts. Monocyte counts for the SF-3000 correlated significantly better with the microscopic counts, whereas correlations of eosinophils and basophils were better for the NE-1500. The efficiency rates of flagging for the presence of ≥ 1% abnormal WBC were 80% for the NE-1500 and 70% for the SF-3000. This difference was exclusively due to low specificity of the SF-3000 in flagging cells of the 'Left Shift' category, especially in samples with elevated WBC counts. The flagging efficiencies for blasts, promyelocytes, myelocytes, atypical lymphocytes and nucleated red cells were identical for both analysers. Thus, with regard to the performance of automated WBC differential counts the SF-3000 seems comparable with other, well established haematology analysers.