Gender differences have not been shown in relation to the immune system in athletic horses. The aim of the present paper was to elucidate gender differences in the non-specific immune response of the polymorphonuclear neutrophil (PMN), plasma glucose and in hormones before and after an exercise in the lactate threshold (LT). A group of 12 Anglo-Arabian horses (6 females and 6 males, 4-7 years old) was observed. A submaximal exercise test was carried out at the LT. The results showed that males had a higher PMN percentage, plasma glucose values, Adherence index (AI) and random migration than females. Also, females showed significant negative correlations between cortisol and catecholamines with PMN and glucose with phagocytosis, and positive ones between AI and catecholamines. In males, negative correlations were established between random migration and chemotaxis with cortisol, and positive ones between cortisol and phagocytosis.