Abstract. Metabolic parameters have been used in an attempt to monitor the health, reproductive and nutritional status of dairy cows. Nevertheless, in the last few years the detection of free radical damage, and the protection against it has become very important in the practice of clinical medicine. This report aims to establish values for plasma lipid hydroperoxides (LOOH) and total antioxidant status (TAS) in healthy cows and its relationship with milk yield. The study was carried out with 22 healthy dairy cows divided into two groups: animals with a low production rate and animals with a high milk yield. Results showed that the animals with a high milk yield present higher LOOH levels than the other group. This increase in oxidant compounds is not accompanied by higher levels in protective antioxidant substances. LOOH and TAS measurements give complementary information about the metabolic status of the animal than metabolic parameters alone.