Immunohistochemical examination of the proliferative activity of cells was made investigating the expression of Ki-67 protein and the location of proteins associated with epithelial cell papillomavirus infection involving P16INK4a and HPV16 proteins in different cell areas of the intact mucosa, in leukoplakia with the signs of hyperplasia and dysplasia, and in squamous cell carcinoma. There was a positive correlation between the proliferative activity of cells in the parabasal cell areas and the expression of P16INK4a protein in oral leukoplakia with the signs of hyperplasia (r