We have expressed an unfused E7 protein from human papillomavirus 16 into Escherichia coli by using a T7-RNA polymerase system. E7 mRNA was detected one hour after promoter induction. Western blot analysis using either a murine monoclonal antibody elicited against E7 or sera from cervical carcinoma patients demonstrated that recombinant E7 expressed in E. coli reacted to both of them, and a 21 kD band is observed as a positive signal. This protein provides a suitable material for further protein structure and immunological studies and offers a screening tool for identification of circulating antibodies in human sera.