A type-specific and neutralizing mouse MAb (V5) against human papillomavirus (HPV) type 16 capsids was found to block the serological reactivity of human sera with the corresponding capsids. Out of 352 human serum samples tested for the presence of IgG against HPV-16, more than 75% of reactive sera were completely blocked by the V5 antibody. Type-specific MAbs against HPV-6, -18 and -33 were also found to block serological reactivity with capsids of the corresponding HPV types for the majority of reactive human sera. The results suggest that most antibodies in human sera that are reactive with intact HPV capsids recognize the same or closely related major antigenic determinant(s).