In elite horses leucocytosis and leucopaenia can be defined as WBC > 10.0 x 109/ L and < 6.0 x 109/ L, respectively. Values lying close to these values should be interpreted with caution given the potentially confusing effects of catecholamine induced mobilisation of cells in this series and the need for appropriate filling of EDTA tubes. Failure to fill correctly can result in an incorrect coagulant to blood ratio with consequently misleading WBC values. Evaluation of the individual components of the WBC series is usually much more informative than reliance on WBC counts in isolation, hence the need for EDTA samples, rather than lithium heparin for haematology as referred to previously.