This study was conducted to assess the pattern of changes and the relative values of homocysteine in bovine tropical theileriosis. The diseased group comprised of 20 cattle (2-3 years old) naturally infected with Theileria annulata. As control group, 10 uninfected cattle were also sampled. Whilecobalt (Co), vitamin B-12, folate, total protein (TP), globulin values were determined significantly lower than control group (P<0.001), serum homocystein (Hcy), creatine kinasemyocardial band (CK-MB), alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine kinase (CK), lactate dehydrogenase (LDH), creatinine, urea, and blood urea nitrogen (BUN) concentrations were determined higher than control group (P<0.001). As a result, decreases in serum B-12 vitamin concentrations of cattle with theileriosis lead to increases in serum Hcy level.