The study aimed at evaluation the effect of dietary supplement of taurine on the oxidation-reduction status in riding horses, and especially on the extent of oxidative DNA degradation in lymphocytes. Ten Thoroughbred and half-bred geldings aged 6-13 years were classified according to breed and amount of work done into two groups - control (C, n=5) and experimental (E, n=5), the latter fed the diet with addition of 40 g taurine/horse/day. Blood samples were withdrawn from the horses' jugular vein before commencing the riding season and then after 30 days of working. In the blood some selected morphological and biochemical indicators were determined including the TBA-RS and 8-oxo-dG in lymphocyte DNA. It was found that physical effort of horses, being used for 30 days in recreation riding, affected homeostasis of redox status, and especially the rate of oxidative DNA degradation of lymphocytes. The addition of taurine to feed caused smaller oxidative stress, manifested by lower concentration of TBA-RS in plasma and of 8-oxo-dG in lymphocytes. The taurine lowered the lipid peroxidation intensity that occurred in horses due to the oxidative stress caused by physical effort. Furthermore, taurine revealed affinity to nucleic acids, counteracted the oxidative DNA degradation and decreased the damages of DNA in lymphocytes.