The authors estimated the concentrations of folic acid and free homocysteine in the blood serum of women with CIN III (cervical intraepithelial neoplasia-Burghard's classification) infected with DNA HPV (human papillomaviruses) of type 16 and/or 18. The control group consisted of 49 patients with normal cytological smears without HPV infection. Types 16 and/or 18 DNA HPV were found in 50 patients. This women qualified for the studied group. The sequence of DNA HPV type 16 and/or 18 was identified with the PCR method (polymerase chain reaction). The high-performance liquid chromatography (HPLC) method was employed to evaluate the levels of folic acid and free homocysteine in the blood serum of the examined patients. Significantly lower levels of folic acid and higher levels of free homocysteine were observed in the blood serum of HPV-positive patients with CIN III. The correlation was found between serum concentrations of folic acid and free homocysteine in both groups.