This study was aimed to investigate erythrocyte arginase activity and plasma nitric oxide (NO) levels in dystocia and normal calving of cows and compare these parameters. The study material consisted of 16 cows, 3–8 years old, brought for parturition at term to the Clinic of Obstetrics and Gynecology at Fırat University. Blood samples of cows normally calving and dystocia were taken into blood collecting tubes with heparin from the jugular vein in the first half hour after delivery and centrifuged at 3000 rpm for 10 minutes. Plasma NO levels and erythrocyte arginase activities were measured. The erythrocyte arginase activity in cows normally calving was significantly increased compared to that in cows with dystocia (P<0.01), and the plasma NO level in cows normally calving was significantly decreased compared to that in cows with dystocia (P<0.05). It was concluded that the lower erythrocyte arginase activity and higher plasma NO level in cows might play a role in dystocia.