The aim of the present study was to determine serum concentrations of the products of nitric oxide oxidation (nitrate and nitrite) and some vitamins (retinol acetate, alpha- and delta-tocopherol, and vitamin D 3) in sheep naturally infected with Babesia ovis. The investigation included 30 infected and 10 control sheep. Serum a- tocopherol levels were significantly lower (P < 0.05), and nitrate and nitrite concentrations were significantly higher (P < 0.05) in infected animals than in controls. It is thought that the elevated nitrate and nitrite levels of the sheep infected with babesiosis were due to the result of damage caused by Babesia. On the other hand, a significant decrease was observed in a- tocopherol levels in sheep with babesiosis because of damage and pathophysiological changes to erythrocytes.