The DNA sequence from a human papillomavirus type 59 (HPV 59) has been recently determined. The HPV 59 genome consists of 7896 nucleotides (nt). A comparative analysis of this sequence with the sequences of other HPVs revealed the closest homology to HPV 18 (71%). To test the transforming activities of HPV 59 DNA and its gene products, several plasmids expressing HPV 59 open reading frames (ORF) were constructed. The E5, E6, and E7 ORFs of HPV 59 were inserted into pRc/CMV vector containing a promoter of cytomegalovirus to test the transforming activities of these ORFs. When these DNAs were transfected into mouse C127 cells, all three ORFs were independently able to transform C127 cells in the presence of G418, although the full length HPV 59 DNAs failed to induce the focus-formation. The E7 ORF showed the strongest transforming activity and the E5 ORF exhibited the weakest transforming activity. Cell lines transformed by E5, E6, and E7 ORFs were established and they grew anchorage-independently. The presence of HPV 59 ORF DNA was confirmed by polymerase chain reaction (PCR) and Southern blot analysis in HPV 59 ORFs-transformed cell lines.