The relationship between human papillomavirus (HPV) infection and cell cycle regulators p53, MDM2, and p21 in cervical intraepithelial neoplasia (CIN) has not been investigated. p53, MDM2, and p21 immunoreactivity were analyzed with respect to HPV DNA status in high-grade CIN (CIN II-III). Formalin-fixed, paraffin-embedded tissue sections from 169 biopsy specimens with high-grade CIN were examined for HPV DNA by polymerase chain reaction with the L1 and E1 consensus primers Gp5+/6+ and CpI/CpIIG. HPV-positive specimens were typed with the E6 type-specific primers for HPV 16 and 18. The biopsy specimens were stained with the monoclonal antibodies p53, MDM2, and p21. The interpretation of nuclear staining was regarded as focal (< 5%), regional (5% to 50%), or diffuse (> 50%). HPV DNA was found in 156 cases (92%); 122 (78%) were positive for HPV 16, 18, or both. Immunohistochemically, p53 was detected in 50 specimens (30%); nuclear staining was mainly focal. Focal nuclear staining for MDM2 was found in 6 specimens (4%), and regional and diffuse nuclear staining for p21 was present in 137 (81%). Significant correlation was found only between p53 and MDM2 immunoreactivity. These results indicate that there is no correlation between HPV status and expression of the cell cycle regulators p53, MDM2, and p21. Inactivation of p21 and p53 protein may be important, and MDM2 abnormalities seem to play a minor role in the development of high-grade CIN.