To determine whether neutralizing antibodies (NAs) against HPV16 is responsible for a higher regression rate of low-grade cervical intraepithelial neoplasia (CIN1), we investigated an association between the presence of the NAs and the fate of the HPV16-related CIN1. All the women examined in this study had HPV16 positive cervix. The women were allocated into four groups by their cervical pathology, i.e., non-pathological (n:7), CIN1 (n:37), CIN2/3 (n:19), and cervical cancer (n:13). Their sera were tested for the presence of NAs against HPV16 by an in vitro assay using HPV16-pseudovirions. As for the CIN1 cases, clinical regression of the lesions were compared between NA-positive and NA-negative groups. Copy number of HPV16-DNA in smear samples was measured by quantitative PCR. The incidence of the presence of the NAs in the women with a nori-pathological cervix (85.7%) was significantly higher than in the CIN1 cases (21.5%), the CIN2/3 cases (15.7%), and the cervical cancer cases (0%) (P < 0.0001). The regression of the CIN1 lesion was closely associated with the presence of the N As (p = 0.0002). The presence of the NAs was associated with low-level copy number of the viral DNA relative to the NA-negative group (p = 0.05). The presence of the NAs against HPV16 was associated with a higher regression rate of HPV-related CIN1 lesions. The NAs seem to have a role in deterring HPV-related cervical lesions from progressing to CIN2/3 by inhibiting the infection with de novo replicated HPV. This study further suggests that HPV vaccine to induce the NAs may be effective in eliminating CIN lesions, especially in the NA-negative cases. (C) 2002 Elsevier Science (USA). All rights reserved.