The E7 gene of human papillomavirus type 16 was expressed in Escherichia coli with a recombinant plasmid prepared previously in our laboratory.The E7 fusion protein produced and purified by gel electrophoresis was used as antigen to immunize rabbits for preparing anti-E7 protein antisera.The antisera were used to stain the tissue sections often cases of uterine cervical cancer with an immunohistochemical technique(colloidal gold labeled stain).The E7 antigen was seen in the cells of 6 cases of cervical carcinoma as black granules under light microscope. The E7 protein was found in the nucleus of positive cells, mainly on the nuclear membrane, arranged in a circle. Only a few silver stained granules were seen in the cytoplasm. We believe that the intracellular distribution of the E7 protein indicates that there is high expression of the E7 gene in the HPV infected cells of the cervical cancer; and the fact that E7 antigen is a nuclear protein suggests that E7 gene is an oncogene of HPV 16.