In an experimental infection of sheep with Theileria lestoquardi some biochemical and haematological parameters were studied in ten Sudanese desert ewes together with 10 clinically healthy ewes. The obtained results showed a significant (P<0.05) decrease in haemoglobin, packed cell volume and white blood cells counts compared to the control group. The decrease in Hb concentrations and PCV% was observed 7-10 weeks after tick application whereas; the decrease in WBCs occurred at week 5 and week 6 after tick application. There was also a significant decrease (P<0.05) in serum total proteins, and serum globulins values of the infected group at week 3- week7 after tick application. A significant increase (P<0.05) in serum urea and serum creatinine values in the infected group was noticed during the first 7-8 weeks in the infected group compared to the control one's. [ABSTRACT FROM AUTHOR]