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The haematological and biochemical changes in Zebu cattle following a natural outbreak of blackleg were investigated at Kachia, Kaduna state, Nigeria. Blood samples (n=20) from each of two herds involved in the outbreak were collected from both the apparently healthy and sick (infected) cattle for analysis. Mean packed cell volume, haemoglobin and total protein concentrations of the sick animals were higher (P<0.001) than those of the apparently healthy ones. There were statistically significant decreases in mean total white blood cell counts (P<0.001) but not in differential leukocyte counts (P>0.001) of the sick animals. Mean free serum sialic acid levels of the sick animals increased (P>0.001), while mean erythrocyte surface sialic acid concentration of the sick animals decreased (P>0.001). Also, there was an increase in the mean neuraminidase activity in the plasma of the in-fected cattle (P<0.001) compared to the apparently healthy ones. The implication of these findings in the pathogenesis of blackleg is discussed