The development of cancer is a multistep process requiring cumulative genetic alterations. An in vit ro model utilizing human cervical cells and papillomaviruses (HPV) that mimics human cervical cancer has been developed. Chromosome and gene alterations associated with distinctive stages of neoplastic transformation were demonstrated with an exocervical cell line obtained after sequential transfection with recombinant HPV-16 DNA and v-Ha-ras oncogene. Acquisition of immortality after HPV-16 transfection was associated with aneuploidy, structural changes of chromosomes 8, 10, 17, 19, 20, and 21, as well as proto-oncogene alterations. HPV-16 DNA was localized to two sites on chromosome 21, with one site at 21q22.2-22.3 near the ets-2 proto-oncogene. Ets-2 as well as c-myc gene mRNA levels were elevated in HPV immortal cells compared to primary nontransfected exocervical strains. Although the HPV-immortalized cells had several features characteristic of malignant cells, they lacked tumorigenic potential. Tumorigenicity occurred after transfection with v-Ha-ras oncogene, which was found stably integrated on chromosome 12 at the telomeric band q24.3. The tumorigenic line had additional clonal chromosomal abnormalities; consisting of multiple deletions involving regions of chromosomes 1p/q, 3p, 9q, loss of one copy of chromosome 11, and a complex rearrangement of chromosomes 8 and 13 as shown by in situ suppression hybridization with whole chromosome probes. Loss of tumor suppressor genes on deleted regions may have contributed to the acquisition of tumorigenicity. The genetic changes observed in these cells parallel those found in cervical carcinomas, demonstrating the validity of the in vitro model for studying the multistep progression resulting in cervical carcinoma.