The authors established the relationship between the indicators of immunohistochemical examination — proliferation markers (Ki67) and mitotic count (pHH3) with the indicators of positron emission tomography — SUVmax. The identified patterns of cancer cells differentiation and their metabolic activity are promising for the diagnosing and screening of tumours of varying degrees of progression and origin, which will allow forecasting the course of the disease at all stages of diagnostics. The study intends to assess the level of oropharyngeal squamous cell histopathological differentiation by immunohistochemical diagnostic methods, and their metabolic activity using positron emission tomography.1. Study of the activity of metabolic processes of transformed oropharyngeal cancer cells using positron emission tomography;2. Determination of tumour proliferative potential by the number of positive stains to Ki-67 (%) and pHH3 by immunohistochemical diagnostic methods;3. Identification of the relationship between morphological changes of oropharyngeal cancer cells and their metabolic activity.Materials and methods. We studied 130 samples of squamous cell carcinoma of the oropharyngeal area. We determined the level of metabolic activity — SUVmax — by positron emission tomography (PET) at the preoperative patient treatment stage. In the postoperative period, the proliferation index (Ki67) and the mitotic count (pHH3) were determined by histological and immunohistochemical methods. Upon assessment of the level of differentiation of tumour cells, patients were divided into three groups: Group I - patients having tumour cells in the G1 phase of mitosis (28 patients); Group II — tumour cells in the G2 phase of mitosis (48 patients); Group III — tumour cells in the G3 phase of mitosis (54 patients). We evaluated PET results according to the Maximum Standard Unit Value (SUVmax).We determined the relationship between morphological changes and metabolic activity of tumour cells by 2- fluoro-[18F]-2-deoxy-D-glucose accumulation and immunohistochemical examination.Results. We established a statistically significant difference between the groups (p<0.001 according to the Kruskal- Wallis test for all indicators). Thus, with decreasing Me level, the differentiation of SUVmax of tumours significantly (p<0.05) increases, which indicates an increase in the degree of malignancy of tumours. We evaluated the results of immunohistochemical examination by Ki67 and pH3 markers in the study groups. Comparing Ki67 and pHH3, a statistically significant difference was found between the groups (p<0.001 according to the Kruskal- Wallis test for all indicators). Thus, with a decrease in the Me level, the differentiation of Ki67 increases significantly (p<0.05), and an increase in pH3 indicates an increase in the degree of malignancy of tumours. Conclusions. We statistically proved the relationship between Ki67, pH3 and SUVmax in oropharyngeal squamous cell carcinoma. We established the possibility of preoperative forcasting of the level of tumour differentiation and the use of pHH3 immunohistochemical marker as a reliable criterion for assessing the level of tumour differentiation, including hardly diagnosable squamous cell carcinoma.