Human papillomavirus (HPV) types 16 and 18 have been identified in two different human cervical carcinomas. The viral DNAs were molecularly cloned and used as probes to screen a large number of genital tumors by Southern blot analysis. HPV-16 or HPV-18 sequences, respectively, were found in a high percentage of cervical carcinomas, but only in a small number of condylomata acuminata or flat condylomas. The majority of the latter lesions, however, contained HPV-6 or HPV-11 sequences, respectively, which in contrast were detected only rarely in carcinomas in situ or invasively growing carcinomas. A similar distribution of the different papillomaviruses was observed when cell swabs taken from the cervix were tested by in situ hybridization.