Papillomaviruses are epitheliotropic non-enveloped double-stranded DNA viruses, whose replication is strictly dependent on the terminally differenti-ating tissue of the epidermis. They induce self-limiting benign tumors of skin and mucosa, which may progress to malignancy (. cervical carci-noma). Prior to entry into basal cells, virions attach to heparan sulfate moieties of the basement membrane.