Introduction. The ozone immune modulation is based on its effect on the immune system and oxidative metabolism. When whole human blood is exposed to the appropriate ozone doses, we can observe in the cells different biochemical reactions that in turn are able to improve the immunity mechanism. Objectives. The aim of this experimental study was to evaluate the effect of ozone on blood phagocytosis. Methods. Blood samples of 30 mL were taken from five healthy male blood donors in the morning, and were subdivided in 6 glass tubes of 5 mL each (control, oxygen and 4 ozone groups). A volume of 5 mL ozone/oxygen mixture at different ozone concentrations (10, 20, 40 and 80 µg/mL) was collected with glass syringes. There after the gas was immediately bubbled in the blood samples. Syringes were slowly but continuously mixed in shaker with stirring, during 10 min allowing a complete mixing of the liquid–gas phases with minimal foaming. Two of the above blood samples were used as controls: the first sample blood and the second blood treated with oxygen only. Phagocytic cell function was assessed by direct microscopic Baehner method. The results were analyzed by paired T test; significance was defined as a value less than 0.05. Results. After ozonation, phagocytic function increase with significant differences in comparison with controls groups (p=0.04). Respect to the ozone concentrations, the phagocytic function increased at 20 µg/mL and even more at 40 µg/mL, but decrease with 80 µg/mL. However, there were no significant differences in phagocytic function in the blood exposed to 10 µg/mL in comparison with controls. Conclusion. Ozone may stimulate the phagocytic function of the peripheral blood cells in a dose-dependent fashion.