Since leukocytes have the potential to produce oxygen free radicals that damage biomolecules, we have evaluated the influence of thiolic antioxidants (glutathione, N-acetylcysteine and thioproline) on selected hematoimmunological characteristics. We used peritoneal leukocytes incubated at 0.5, 1.0 and 5.0 mM concentration of antioxidants. Following thiol treatment, we found a stimulation of phagocytic activity, and markedly decreased incidence of programmed cell death of peritoneal leukocytes, both basal and induced by H₂O₂. Low concentrations of thiolic compounds also increased the activity of catalase, glutathione peroxidase and glutathione reductase. On the contrary, only the highest concentration of N-acetylcysteine and thioproline reduced superoxide dismutase activity. Tested antioxidants can lead to a decrease of the oxidative stress, and could provide a nutritional benefit for evaluated immunological characteristics.