Results reported in the present study indicate that in addition to changes in blood gas parameters comparable to SET patterns previously found in the athlete horse [11], moderate physical exercise modulates NO production. Furthermore, NO production and body temperature are correlated after moderate exercise thereby suggesting a complex physiological response aimed at facilitating post- exercise recovery. All the blood parameters evaluated were significantly modified at short times after SET of moderate intensity with most relevant changes observed for Hct. This was probably caused by the combined effects of the in- crease in sweating and splenic recruitment of erythrocytes occurring during SET.