Human papillomaviruses (HPV) 16 and 18 are closely linked with human genital cancer. In most cervical carcinomas, viral sequences are integrated into the host genome. HeLa, a cervical carcinoma cell line, has multiple copies of integrated HPV 18 DNA. In this study, in situ chromosome hybridization was used to assign the integration sites of HPV 18 DNA sequences on HeLa cell chromosomes. Four sites of hybridization were identified at 8q23----q24, 9q31----q34, p11----p13 on an abnormal chromosome 5, and q12----q13 on an abnormal 22. Three of these sites correspond with the locations of MYC, ABL, and SIS protooncogenes, and are at or in close proximity to fragile sites. The chromosomal localization of HPV 18 DNA may be useful in assessing the role of viral integration in the development of this malignancy.