Introduction. Reading reference ozone books from Dra. Menendez, Dra. Viebhan, Dra. Borrelli and Dr. Bocci, proper timing for mixing ozone in blood during autohemotherapy is not calculated in a scientific way, having only an estimation of it based on changes in the blood color, more related to oxygen absorption than on ozone itself. Material and methods. We decided to reproduce a reduced model of great autohemotherapy or recently renamed as systemic indirect endovenous ozonotherapy (SIEVO) by the World Federation of Ozone Therapy ? WFOT, using syringes to simplify the experiment. Our model consisted of a 20 mL syringe filled with 10 mL of blood withdrawn from healthy volunteers and mixed it gently but in controlled way with 10 mL medical ozone at different concentrations; after 5 and 8 seconds, the remaining gas was analyzed by an spectrophotometer based ozone detector to check the amount of ozone. Data were analyzed using a linear regression model. Results. Results show that even for 60 mcgr/mL ozone concentration, 8 seconds is enough to let all ozone absorbed in blood. Discussion and Conclusions. The experiment shows how quick ozone reacts with blood and claims for a trial with real SIEVO devices to achieve a real timing.