The Abbott Cell Dyn (CD) 3000 is an automatic analyser, designed to give a complete blood count (CBC) and white blood cell differential (WBCD) by 4 angle diffraction analysis. This instrument was evaluated by comparison of results obtained with those obtained from a Technicon H1 analyser and by microscopic examination. Technical performances with regard to reproducibility, linearity and carryover was acceptable and in normal samples there was close correlation with the optical method (R > 0.9) for neutrophils (NE), lymphocytes (LY) and eosinophils (EO). Correlation for monocytes (MO) and basophils (BA) was poorer but without clinical consequences. Significant thresholds for immature granulocyte (IG) and variant lymphocyte (VL) flags were determined and using these thresholds the false positive rate was reduced to 7%. In haematological diseases, no false negatives were observed as all samples were flagged. However, since no case of acute lymphoblastic leukaemia (ALL) was studied, the detection of lymphoblasts which is known to present difficulties for analysers remains to be evaluated. Blasts in acute myeloblastic leukaemia (AML) and hairy cells were recognised, while in chronic lymphocytic leukaemia (CLL) it was possible to define 3 groups according to the flags released. The CD appears to be a satisfactory analyser for use in general or haematological laboratories performing a large number of WBCD per day.