The close association between human papillomavirus type 16 and cervical cancer implies some role for the virus in the development of this cancer. It has been demonstrated that HPV-16 DNA sequences in the presence of activated ras are capable of transforming primary baby rat kidney cells. This communication describes the characterization of these transformed cells. All cell lines are shown to be tumorigenic in immunocompetent rats and there is continued expression of the HPV-16 E6 and E7 polypeptides in a number of the cell lines analyzed, suggesting a role for at least one of these proteins in the maintenance of the transformed phenotype.