The aim - in the given research, the difficulties in interpreting the study results of oxidative homeostasis of oral fluid are analyzed. Changes in the total antioxidant activity of blood and saliva can be multidirectional - an increase or decrease in the oral fluid indicator and a reduction in the parameter of blood plasma can be recorded. To resolve the emerging difficulties, there was proposed a parallel assessment of the dynamics of changes in the total antioxidant activity of blood plasma and oral fluid in the patients of 4 groups with nosological forms of fundamentally different in the distribution and localization of the pathological process, which include: phlegmons of the maxillofacial region, partial absence of teeth, type 2 diabetes mellitus and the pelvic inflammatory diseases. As a result of the conducted studies, it was shown that a simultaneous decrease in the total antioxidant activity of blood plasma and oral fluid was attributable to the chronic long-term somatic diseases of a systemic character with a significant metabolic disorder, such as type 2 diabetes mellitus. A decrease in the total antioxidant activity of blood plasma and the unchanged oral fluid index was characteristic of somatic diseases of limited prevalence without affection of the maxillofacial region's tissues. In our case, such an example was a chronic inflammatory disease of the uterus with a combined course of bilateral salpingoophoritis. An increase in the oral fluid's total antioxidant activity on the background of a normal or even slightly reduced level of the antioxidant potential of blood plasma was characteristic of dental diseases. The latter situation was most likely for the dental profile diseases, in which damage to the oral tissues can provoke the leaching of cellular contents, including endogenous antioxidants or other components of regenerative activity in the oral fluid. Herein, changes in the antioxidant activity of blood plasma may reflect the prevalence of a pathological process at the systemic level or its limitation only to the dentoalveolar system's tissues and elements. As an example of such a situation, the patients with phlegmon of the maxillofacial region or patients with partial absence of teeth can be cited.