The protein product of the retinoblastoma tumor suppressor gene (pRb) has been demonstrated to bind transcriptional factors such as E2F and c-Myc protein in vitro. To determine whether pRb regulates both cellular (c-myc) and viral (HPV LCR) promoter activity in vivo, MYC-CAT or HPV LCR-CAT chimeric expression plasmids were generated and cotransfected with a pCMV-RB expression plasmid. pRb repressed both myc and LCR transcription but not SV40-CAT. Transcriptional repression induced by pCMV-RB was relieved by addition of pSV2-E7. Moreover, immunohistochemical assays indicate that in cervical intraepithelial neoplasia lesions, an increased pRb expression correlates with decreased c-myc oncogene expression. These results suggest that pRb can negatively regulate c-myc transcription in vivo in both normal tissue or early cervical lesions. However, in HPV induced invasive cervical carcinomas where viral DNA is integrated expressing its oncoproteins, pRb could be complexed by HPV E7 oncoprotein releasing the repression effect and promoting cell growth.