Human papillomaviruses (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 tumours by Southern blot analysis. HPV 16 or HPV 18 sequences 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 carcinoma in situ or invasive carcinomas. A similar distribution of the different papillomaviruses was observed when cell scrapings taken from the cervix were tested by in situ hybridization.