32P-labelled cloned HPV 6 DNA was used as probe to analyze human genital tumors for DNA sequences homologous to HPV 6 DNA. Ninety three percent of all condylomata acuminata (41 out of 44) were found to harbor HPV 6 DNA. Of the remaining three, one contained HPV 1 DNA. No papillomavirus DNA was identified in the two other tumors. All three invasively growing giant condylomata acuminata (Buschke-Löwenstein tumors) investigated also contained HPV 6 DNA. Two out of six atypical condylomata of the cervix hybridized with HPV 6 DNA under stringent conditions, one only under conditions of low stringency. All DNA preparations from malignant tumors studies (54 cervical carcinomas, 10 penile carcinomas, two vulvar carcinomas) failed to anneal with HPV 6 DNA, even under conditions of low stringency. Although all HPV 6-positive condylomata acuminata analyzed in this study revealed HPV 6 DNA of regular molecular weight (5.1 x 10(6)), two of the Buschke-Löwenstein tumors, as well as one of the two positive atypical condylomata of the cervix, contained HPV 6 DNA with a remarkable size classes occurred in a supercoiled form without evidence for integration into host cell DNA.