We have developed a sensitive and specific ELISA method using the s10-fusion proteins of human papillomavirus (HPV) 16 E6 and E7, expressed in E. coli. Sera from 97 women (30 patients with invasive cervical cancers, 26 patients with cervical intraepithelial neoplasia III (CIN III) and 38 healthy women) were tested for the presence of antibodies to E6 and E7 proteins. Eight (27%) of the 30 cervical cancer sera, five (19%) of the 26 CIN sera and none of the 38 normal sera were reactive with E6 proteins (cut-off point: absorbance (A) = 0.59, x +3SD). Ten (33%) of the 30 cervical cancer sera, two (8%) of the 26 CIN III sera and none of the 38 normal sera were reactive with E7 proteins (cut-off point: A = 0.40, x +3SD). The mean absorbance for anti-E7 antibody in positive cases was higher in cancer patients than in CIN III patients, while that for E6 did not differ between these two groups. Interestingly, six (50%) of 12 cancer sera which reacted with either E6 or E7 proteins were reactive for both proteins, whereas none of the sera from the CIN III patients reacted with both proteins. The high prevalence rates and high absorbance values for HPV 16 E6 and E7 antibodies in association with malignant transformation suggest that detection of these antibodies may be a useful diagnostic aid for cervical cancer-associated HPV 16.