SUMMARYThe presence of human papillomavirus (HPV) type 16 DNA in biopsies from precancerous lesions and from early lesions of human cervical cancer, and the integration of virus DNA into host cell DNA were analysed by dot blot and Southern blot hybridizations. HPV 16 DNA was detected in 23~ of mild dysplasias, 329/o of moderate dysplasias, 55 ~ of severe dysplasias and 62 ~ of carcinomas in situ by dot blot hybridization. Digestion of the DNA with restriction enzymes PstI and BamHI followed by Southern blot analysis revealed the presence of some typical restriction fragments of HPV 16 DNA in most virus-positive samples. In addition, we detected submolar fragments which might represent virus-cell junction sequences in 869/oo of dysplasias, suggesting that the integration of HPV 16 DNA could occur in the precancerous stage.Human papillomavirus (HPV) type 16 and type 18 DNAs are frequently found in biopsies from precancerous and malignant cervical lesions (Boshart et al., 1984;Crum et al., 1985;Lehn et al., 1985;Tomita et al., 1986), with HPV 16 DNA being more common than HPV 18 DNA in these lesions (Diirst et al., 1983 ;Boshart et al., 1984;Yoshikawa et al., 1985). HPV 16 DNA has been cloned from an invasive cervical carcinoma (Dtirst et al., 1983) and the complete nucleotide sequence was determined (Seedorf et al., 1985). Recently, Diirst et al. (1985) reported the physical state of HPV 16 DNA in some malignant turnouts and showed that the integration of HPV 16 genome into the host cell DNA occurs with a head-to-tail viral genome arrangement. Their report includes a discussion of HPV integration in connection with the causative event in malignant transformation.Dysplasias are considered to be precancerous lesions and are classified as mild, moderate and severe (Koss, 1978). In order to see whether the integration of HPV 16 DNA into host cell DNA occurs in precancerous lesions, biopsy samples from mild, moderate and severe dysplasias and from cervical cancers were screened for the presence of HPV 16 DNA by dot blot hybridization. Virus-specific restriction fragments were analysed by Southern blot hybridization. We report here the detection of submolar fragments, which might be virus-cell junction sequences, in most dysplasias and carcinomas in situ that harbour HPV 16 DNA.Biopsy samples were collected under colposcopy and kept at -70 °C. High molecular weight DNA was extracted and purified from samples that had been histopathologically confirmed (Tomita et al., 1986). For dot blot hybridization, about 7.5 p.g of the purified DNA was denatured, neutralized, then spotted onto a nitrocellulose filter and hybridized with 32p-labelled cloned HPV 16 DNA in 6 x SSC at 68 °C for 24 h. The specific activity of the HPV 16 DNA was 108 to 2 x 108 c.p.m./~tg. The filter was washed extensively with 0