This study was performed to determine changes in serum NO (nitric oxide) levels in cattle with theileriosis in accordance with PCV levels. For this purpose, 42 cattle with theileriosis and 10 healthy cattle have been used as material. Infected animals have been divided into 3 equal groups. 1^st group had <12%, 2^nd group had 13–24% and 3^rd group had <25% PCV level. Blood samples have been used to determine NO concentrations. Serum NO concentrations prior to treatment increased in all infected groups compared to control group however its levels were significant only in the third group. NO concentrations decreased to almost normal values after treatment especially in 2^nd and 3^rd group, however this decrease was not significant in the first group. As a result, NO levels have been found increased in cattle with natural theileriosis. Therefore, its concluded that NO level and PCV levels in theileriosis should be studied with more detail in the future to enlighten the role of NO release and strategies for controlling its’ release should be made especially in severe cases.

Key words: Anaemia, Cattle, Nitric oxide, Packed cell volume, Theileriosis