Human papillomavirus (HPV) is found in close association with carcinogenesis of the uterine cervix. We applied a new in vitro gene amplification technology, the polymerase chain reaction (PCR) to detect HPV 16 and 18 in cervical exfoliated cells. HPV infections were detected in 5 (16%) of 31 women with no pathological lesions of the uterine cervix (normal), 16 (24%) of 67 with cervical intraepithelial neoplasia (CIN) and 6 (38%) of 16 with invasive cervical cancer. Moreover, 10% formalin-fixed and paraffin-embedded tissue sections were prepared from the uterine cervix of these 27 women with PCR-proven HPV infection and were examined for the histological localization of HPV-DNA by in situ hybridization with biotin-labeled DNA probes of HPV types 6/11, 16/18 and 31/33/35. HPV-DNA type 16/18 was detected in 3 of 5 normal women, 2 of 4 CINs I, 2 of 3 CINs II, 6 of 9 CINs III and 6 of 6 invasive cervical cancers. HPV-DNA type 6/11 was detected in 6 of 6 condylomas. Viral DNA sequence was detected in the superficial cells of CIN I and II, and it was distributed through entire thickness layer of undifferentiated cells derived from CIN III and squamous cell carcinoma. In addition, the staining intensity became weak as the lesion progressed. These differences between lesions might be due to the difference in the viral form in the nuclei, ie whether an episomal or integrated form. Thus, an in situ hybridization technique with a biotin-labeled DNA probe as well as the PCR method is useful for the detection of HPV in clinical samples.