In this study, 32 thoroughbred English and 32 thoroughbred Arabic horses from Turkish Jockey Club (Veli Efendi), that participated racing in 1999-2000 race season were used. In blood samples, leucocyte, erythrocyte, thrombocyte. lymphocyte, monocyte and granulocyte counts, lymphocyte, monocyte, granulocyie and haematocrit percentage (plasma cell volume) and the haemoglobine ratio were studied. The erythrocyte phase indices (MCV. MCH. MCHC) were then calculated. No significant differences were found between two groups.