A series of human carcinoma cell lines was examined for human papillomavirus (HPV) DNA sequences with the use of HPV-6, HPV-11, HPV-16, and HPV-18 DNA probes. Six of eight cell lines derived from human cervical carcinomas were shown to contain integrated HPV DNA sequences. In five of these six lines, HPV-specific polyadenylated RNA species could also be identified. The expression of HPV sequences was detected in three lines with a HPV-18 DNA probe and in two lines with a HPV-16 DNA probe. Of the two lines which contained HPV-16 specific RNA, one contained HPV DNA sequences which hybridized only to an HPV-16 probe, and the other contained HPV DNA sequences which hybridized to both HPV-16 and HPV-18 DNA probes. Six cell lines established from human squamous-cell carcinomas of the bladder, pharynx, lung, esophagus, and vulva were negative for HPV-6, HPV-11, HPV-16, and HPV-18 DNA sequences under stringent hybridization conditions.