To determine the number and isotype of immunoglobulin (Ig)-containing cells that infiltrate various stages of cervical neoplasia from no lesion to invasive cancer. By three-color immunofluorescent microscopy, the number and isotype of stromal plasma cells were determined for 91 specimens representing a spectrum of cervical epithelial neoplasia as follows: no lesion (n=12), koilocytic atypia (n=13), mild dysplasia (n=21), high-grade squamous intraepithelial lesions (SIL; n=22), and invasive carcinoma (n=23). The Ig-positive cell counts were markedly increased under the low-grade SIL. Specifically, the mean number of IgG-positive plasma cells was significantly increased (P < .003) under the subepithelial stroma of mild dysplasia as compared with no SIL, high-grade SIL, or invasive carcinoma. These immunocyte infiltrates were clustered in the stroma beneath koilocytes, which also demonstrated IgG-positive intracellular staining. Low-grade cervical lesions are infiltrated by IgG plasma cells to a greater extent than high-grade or invasive cervical lesions, suggesting that antibody responses are preferentially recruited in early cervical neoplasia, giving credence to the concept that low-grade lesions represent a human papillomavirus infection of the cervix rather than a neoplastic condition.