Human papillomaviruses (HPVs) have been strongly linked to progression of human cancers, such as cervical and oral cancers. Two HPV oncoproteins, E6 and E7, can inhibit the tumor suppressor proteins, p53 and pRB, respectively, resulting in a deregulation of the cell cycle. In order to further test the significance of HPV expression in oral and cervical carcinogenesis, we analyzed HPV E7 mRNA in oral and cervical neoplasia and cell lines by reverse transcriptase-polymerase chain reaction (RT-PCR). We found that HPV E7 mRNA was present in 90% of patients with oral neoplasia and 100% of patients with cervical neoplasia. Quantitative RT-PCR and western blot analysis on both transformed cervical and oral epithelial cell lines demonstrated that the mRNA level of HPV-16 E7 corresponded to E7 protein level, suggesting that HPV oncogene expression is primarily regulated at the transcriptional or post-transcription level. The potential clinical application of quantitative RT-PCR for HPV E7 mRNA expression in cancer screening and treatment evaluation requires further investigation.