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In the course of in vitro systems search for the toxicity screening of plant extracts, different cellular models have been applied to examine their adverse effects in our previous studies. In this study, the main aim was to assess the dose-dependent pro- and antioxidant potential of four species and one interspecific hybrid of Thymus genus sampled in the western part of Ukraine on human erythrocytes' model. For this purpose, we used 2-thiobarbituric acid reactive substances (TBARS) as a biomarker of lipid peroxidation used as an assessment of oxidative stress in erythrocytes' suspension after incubation with plant extracts in two doses (5 mg/mL and 0.5 mg/mL). An erythrocytes’ suspension at 1% hematocrit was incubated with 4 mM phosphate buffer (pH 7.4) (control) and pre-incubated with the extracts (5 mg/mL and 0.5 mg/mL, respectively) at 37 °C for 60 min. The treatment by extracts obtained from various plants belonging to the Thymus genus in dose 5 mg/mL increased the TBARS level as a biomarker of lipid peroxidation in the human erythrocyte suspension when compared to untreated erythrocytes. The most potent prooxidative effect was demonstrated by the Th. alpestris Tausch ex A. Kern., Th. serphyllum L., Th. x porcii Borbás, and Th. pannonicus All. compared to phosphate buffer as a control samples. The minimum increase of TBARS content in human erythrocyte suspension was induced by Th. pulegioides L. extract. In the case of dose 0.5 mg/mL, Th. alpestris, Th. pannonicus, Th. x porcii caused also increased the TBARS level (by 58 %, 51 %, 43.1 %, p<0.05, respectively) compared to untreated erythrocytes. On the other hand, Th. serphyllum and Th. pulegioides extracts decreased the TBARS level (by 16.5 and 2.7 %, respectively), but these changes were no significant. Moreover, Th. serphyllum extract in dose 0.5 mg/mL caused the increase of TBARS level (by 48.8 %, p<0.05) compared to those in dose 5 mg/mL. The extracts obtained from leaves of Th. alpestris, Th. pannonicus, and Th. x porcii in both doses (5 and 0.5 mg/mL) has a mild cytotoxic activity on the human erythrocytes increasing the level of lipid peroxidation biomarker. These findings suggest that Th. alpestris, Th. pannonicus, Th. x porcii extracts possessed prooxidant effects in both doses, while effects of Th. serphyllum and Th. pulegioides extracts to erythrocyte suspension were dose-dependent. Further research is needed to determine the effects of the active compounds of various plants belonging to the Thymus genus on erythrocytes' metabolism.