Experiments on rats showed that complete Freund's adjuvant-induced low-grade fever and pyrogenal-induced fever of different duration are accompanied by an increase in the content of lipid peroxidation products and components of the antioxidant system not only in blood plasma, but also in the central lymph. These changes reflect activation of drainage, evacuation, and transport function of the lymphatic system. We conclude that the lymphatic system plays an important role in the maintenance of the prooxidant-antioxidant balance under these pathological conditions.