Some antipsychotics, including ziprasidone (ZIP), contribute to pro- and antioxidative imbalance in schizophrenic patients. Therefore, searching for effective antioxidative supplementation decreasing antipsychotics prooxidative effects has a high clinical importance. The aim of the study was to establish the effect of ZIP on human plasma – by determining the levels of thiobarbituric acid reactive substances (TBARS), in in vitro model. Material and methods: Blood samples were obtained from healthy male volunteers and placed in the ACD solution. The active substance, i.e. ZIP, was dissolved in 0.01% solution of dimethylsulfoxide to reach the final concentrations (40 ng/ml, 139 ng/ml) and incubated with plasma (for 1 and 24 hours at 37°C). Plasma was also incubated with quercetine (7.5 μg/ml, 15 μg/ml) and with quercetine and ZIP, in different combinations of tested concentrations. Control samples (without the drug) were performed for each experiment. TBARS concentrations were determined using Rice-Evansspectrophotometric method (modified by Wachowicz and Kustroń). Results: ZIP at the concentrations of 40 ng/ml and 139 ng/ml after 24 hours of incubation with plasma causes an increase in TBARS (p respectively <0.01 and <0.002). Quercetine (7.5 μg/ml, 15 μg/ml) incubated for 24 hours in plasma with ZIP decreases lipid peroxidation on average by 38% (for ZIP 40 ng/ml p respectively <0.0003 and <0.0001, for ZIP 139 ng/ml p respectively <0.002 and <0.004). Conclusions: Quercetine significantly decreases lipid peroxidation induced by ziprasidone.