Human papillomaviruses (HPVs), especially types 16 and 18, are strongly associated with the development of cervical intraepithelial neoplasia (CIN) and invasive carcinoma. The HPV E6 and E7 proteins are expressed constitutively in the majority of CIN lesions and carcinomas. Therefore, they are targets for the immune response against HPV and candidates for active immunotherapy. We have previously detected HPV-specific CTLs from the peripheral blood mononuclear cells from a cervical cancer patient following immunization with a recombinant vaccinia using in vitro restimulation with adenovirus recombinants expressing HPV16 or HPV18 E6/E7 fusion proteins. In this study, we used a similar protocol to determine the prevalence of CTL responses against HPV16 and HPV18 E6/E7 in the peripheral blood mononuclear cells from 10 CIN III and 10 normal subjects. HPV-specific CTL responses were detected in 6 of 10 CIN III subjects. These CTL lines recognized HPV16 E6/E7 proteins presented by at least three MHC class 1 HLA alleles and by HPV-transformed CaSki cells. No HPV-specific CTLs were detected in normal subjects. This study demonstrates the presence of naturally occurring HPV-specific memory CTLs in a majority of CIN III patients and provides an approach for further study of their role in modulating cervical malignancy.