In 2108 sheep proceeding from 62 flocks from the Zaragoza province, the glutathione peroxidase activity was determined in blood. Twelve out of the 62 flocks (19.3%), corresponding to various veterinary zones, showed GSH-Px activities higher than 120 U/g Hb and in 35 (56.5%), distributed equally in different zones, none of the sheep showed activities lower than 60 U/g Hb. A 6.5% (4 flocks) showed clearly deficient levels (<60 U/g Hb). The flocks with deficient or marginal levels were located mainly in the Ebro bank, in the areas with higher altitude in the north of the Zaragoza province as in the zone near to the Moncayo hill and in the feet of the Iberian System.