Human papillomavirus type 60 (HPV-60) is the only virus type that has been identified in epidermoid cysts. In this study, HPV-57 DNA was found in three out of 18 plantar epidermoid cysts with different histological features from HPV-60-associated cysts, using PCR and Southern hybridization. The HPV-57-associated cysts had features resembling an HPV-2-specific cytopathic effect. The sequences of two HPV-57 DNA clones isolated from two patients were identical, but differed at some positions from those of HPV-57a and HPV-57b. This putative new subtype was tentatively designated as HPV-57c, and may be associated with plantar epidermoid cysts showing histological features resembling the HPV-2 cytopathic effect.Human papillomavirus (HPV) has recently been identified frequently in palmoplantar epidermoid cysts (Egawa et al., 1987(Egawa et al., , 1990(Egawa et al., , 1995Kimura et al., 1987 ;Matsukura et al., 1992), suggesting that HPV may play a role in the pathogenesis of these cysts, and HPV-60 is the only HPV type that has been identified in epidermoid cysts so far (Matsukura et al., 1992 ; Egawa et al., 1994 Egawa et al., , 1995Kawase et al., 1994). It has also been well-established that homogeneous intracytoplasmic inclusion bodies in the cyst wall and vacuolar structures in the cyst cavity are pathognomonic for HPV-60 infection in the cysts (Matsukura et al., 1992 ; Egawa et al., 1993 Egawa et al., a, 1994 Egawa et al., , 1995.Here we have isolated a putative new HPV-57 subtype from plantar epidermoid cysts using PCR and Southern 9349. e-mail hkita!med.kitasato-u.ac.jp hybridization. Instead of intracytoplasmic inclusion bodies and vacuolar structures, the histological features of the HPV-57-associated cysts were like those of the HPV-2-specific cytopathic effect (Gross et al., 1982 ;Jablonska et al., 1985). We have previously found a plantar epidermoid cyst with inverted growth, which histologically showed HPV-2-related features (Egawa et al., 1993 b), and we identified an HPV-57 DNA fragment using PCR (Egawa et al., 1998). To establish whether that was an isolated finding or a reflection of a close relationship between HPV-57 and plantar epidermoid cysts, we searched for HPV-57 in 18 plantar epidermoid cysts with histological features similar to those of the first HPV-57-related case, using PCR and Southern hybridization. Sequencing analysis of the amplified HPV-57 DNA fragments was also performed and sequences of cysts were compared with each other and with those of two reported HPV-57 subtypes, HPV-57a and HPV57b.Sections (4 µm) were serially prepared from formalin-fixed and paraffin-embedded specimens of the 18 epidermoid cysts and were stained with haematoxylin-eosin for conventional histological studies. On microscopy, instead of intracytoplasmic homogeneous inclusion bodies in the cyst wall or vacuolar structures within the keratinous mass, which are pathognomonic for HPV-60-related epidermoid cysts, the characteristic histological features of these cysts were vacuolated cells or condensed kera...