Genus gamma-papillomavirus consists of HPV 4, 48, 50, 60, 65, 88 and 95, while genus mu HPV 1 and 63.  A characteristic of these genera is producing various intracytoplasimic inclusion bodies (ICBs) in genotype-specific manner. Recent data suggest that the heterogeneous ICBs, and their association with specific types of HPV, will provide a useful model for studying the interaction between keratinocytes and HPVs, especially in the functional aspect of E4 gene expression.  Aside from the HPV type-specific ICBs, HPV 4/60/65-associated pigmented warts implicate HPV type-specific activation of melanogenesis; HPV 60 provides a new clinical entity of HPV-associated epidermoid cysts; a reported double infection with HPV 1 and HPV 63 within a single cell with only HPV 63-associated ICB poses an important problem of a possible interference between the viruses; HPV 63-induced punctate wart has recently been described as an excellent clue to epidermal stem cells whose exact localization is not yet clear; and HPV 1-induced hypertrichosis observed in a patient suggests that HPV infection not only induce visible lesions but also activate its neighboring epithelium. The genus gamma- and mu-papillomaviruses thus pose important problems to be resolved in virology and human pathology.