The regularities of the effect of histamine in concentrations of 0.01; 0.1; 1; 10 μM were studied and quercetin in concentrations of 0.1; 0.3; 0.5; 1; 3; 5 mM, as well as their combined effect on the prooxidant-antioxidant state of blood plasma of rats, using cluster and factor biometric analyses. It was established that the experimental groups according to the investigated indicators (TBА-positive products, lipid hydroperoxides, carbonyl groups of neutral and basic proteins, superoxide anion radical, superoxide dismutase, catalase, reduced glutathione, ATP) were distributed among 13 clusters (according to cluster analysis). In one group of similarities, the effect of histamine in concentrations of 0.01 µM and 1 µM was revealed. Quercetin at a concentration of 0.5 mM and histamine at a concentration of 0.1 µM have a similar effect on the indicators of the prоoxidant-antioxidant state of the blood plasma. Combined addition to the blood of histamine at a concentration of 10 μM and quercetin at a concentration of 0.1; 0.5; 3 mM lead to the same changes in the indicated studied indicators. Cluster analysis also combined the combined effects of 0.01 μM histamine and 0.1 and 3 mM quercetin. It is important to note that a decrease in the content of carbonyl groups of proteins was found in those classers whose experimental blood groups were added to histamine and quercetin, which indicates a decrease in protein damage due to free radical oxidation processes. Using factor analysis, it was established the presence of three hidden factors that affect the processes of free radical oxidation of blood under the action of histamine and quercetin. A high correlation of factor I with protein carbonyl groups, reduced glutathione, superoxide anion radical was revealed. Factor II is most correlated with ATP, superoxide dismutase, lipid hydroperoxides. There is a close relationship between factor III and TBА-positive products and catalase. Taking into account the closeness of the relationship, factor I was given the name “factor of action on proteins”, factor II – “factor of action on bioenergetics and initiator of lipid peroxidation processes”, factor III – “factor of enhancement of lipid peroxidation processes”. It was established that quercetin activates factor I (influence on proteins, causing their oxidation) and factor III (intensification of lipid peroxidation processes) depending on the concentration of the drug. Quercetin in a concentration of 1 mM has the property of both factors (I and III).