To explore the role of Human papillomavirus (HPV) in mammary carcinogenesis, the expression of the HPV-16, iNOS, P53 and hTERT proteins in breast carcinomas and their relationships were investigated. 52 samples of breast cancer and 16 samples of benign breast tumors were assayed using the immunohistochemical SP method for detection of protein expression levels. The expression of HPV-16, iNOS, P53 and hTERT proteins in a mammary carcinoma was 44.2%, 57.7%, 63.5% and 59.6% respectively, which was significantly greater than the corresponding levels in the benign group. The expression of iNOS, P53 and hTERT was correlated with the presence of an HPV-16 infection in a mammary carcinoma (P