Several benign and malignant skin tumors were analyzed for the presence of human papillomavirus (HPV) DNA. By hybridization with different HPV DNA probes under non-stringent conditions (Tm -40 degrees C), two tumors were found to contain HPV-specific DNA sequences in high copy numbers: (1) a keratoacanthoma from a patient who also suffered from a basalioma; (2) a superficial spreading malignant melanoma of an immunosuppressed patient. For further analysis of these DNA sequences genomic libraries from both tumor DNAs were constructed and, out of these, 4 different HPV DNA types have been cloned. By cross-hybridization experiments and restriction map analysis HPV 9 DNA was identified in the keratoacanthoma whereas HPV 17a DNA could be cloned from the malignant melanoma. From each tumor one additional HPV-type not identical to other known HPV-types was cloned. These isolates are closely related to HPV 9, 15, 17, 22 and 23. A physical map of both HPV DNAs was constructed. Size (7.8 kbp), co-linear alignment to HPV 16, cross-hybridization with other HPV-types under conditions of low stringency and monomeric episomal state of the HPV molecules indicate that these two DNA probes represent new HPV types that have been tentatively designated as HPV 37 (keratoacanthoma) and HPV 38 (malignant melanoma). None of these two HPV types could be found in any other of 231 tumor DNAs originating from different tissues.