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Middle ear cholesteatoma is a cyst like structure composed of keratinizing squamous epithelium that contains keratin debris and subepithelial connective tissue. Bone resorption may lead to destruction of ossicular chain and temporal bone. The higher activity of N-acetyl-beta3-glucosaminidase (HEX) was noted in cholesteatoma tissue, compared to the controls. It is supposed, that HEX takes part in bone resorption in middle ear cholesteatoma. Using of HEX inhibitors in cultured fibroblasts and evaluation HEX mRNA expression may contribute to showing new ways of understanding cholesteatoma pathogenesis.was to elaborate cholesteatoma fibroblast cell culture (CF) technique and evaluate in vitro inhibition potential of pyrimethamine.Cholesteatoma and normal retroauricular skin sample obtained during surgical treatment were used in the study. CF served as a study group and fibroblast derived from skin specimens--as controls. Pyrimethamine was used at the concentrations of 1.5, 3, 10 and 20 microg/ml. The reverse transcriptase-polymerase chain reaction (RT-PCR) was carried out for the determination of HEX gene expression.RT-PCR established the elevated expression of HEXA and HEXB mRNA in cholesteatoma. HEXA mRNA in CF was six times higher than in the controls. HEX mRNA expression found to be regulated by pyrimethamine. Inhibition of HEXA and HEXB mRNA expression was achieved when the highest concentration of PYR was used. Low concentrations of pyrimethamine upregulated HEX gene in CF.Pyrimethamine, depending on its concentration, contributes to regulating the HEX gene expression in CF and controls. Pyrimethamine may be regarded as a new future research direction on factors, that may limit development of cholesteatoma.