Certain HPV types have been linked to the genesis and development of premalignant and malignant skin diseases. There have been several contradictory reports on the role of HPV infections in the development of keratoacanthomas (KAs). To further study the involvement of HPVs in the aetiology of KAs, we investigated paraffin-embedded specimens of 80 biopsies of KAs for the presence of HPV 1, 2, 3, 4, 5, 7, 26, 37, 38, 47 and 59 DNA by in situ hybridization (ISH) with biotinylated probes under high stringency conditions (Tm-10 degrees C). Every fourth biopsy specimens was also examined by polymerase chain reaction (PCR) with consensus primers targeting the HPV E1 and L1 regions. The positive cases were further studied by direct DNA sequencing. All specimens proved to be negative for all HPV DNAs studied by ISH. Three out of 20 cases produced in positive PCR amplifications when consensus primers targeting the L1 region were used. However, the same samples remained negative with general primers targeting the E1 region. The DNA sequence analysis of the PCR-positive products showed a 76% homology with HPV type 17. Our results suggest that the known HPV types are unlikely to have any role in the aetiology of KAs.