For many years it has been thought that a significant proportion of cervical cancer could be attributed to sexually transmitted agents, such as sperm, smegma, Treponema pallidum, Gonococcus and herpes simplexvirus type 2. Recent advances of molecular biology, however, have revealed that human papillomavirus (HPV) might be the most causative virus of the disease. Since HPV type 16 DNA was found in a patient with cervical cancer in 1983, many HPV types have been cloned from cervical cancers, also from premalignant lesions (intraepithelial neoplasias). In Japan, we have found 6 new types of HPV (HPV 58, 59, 61, 62, 64, 67) in the female genital tract so far. Especially, HPV 58, which was cloned from a patient with cervical squamous cell carcinoma and was already fully sequenced, is thought to be an important agent for the development of cervical cancer as well as HPV 16. Now we are investigating extensively to clarify the real relationship between genital HPV infection and cervical cancer.