Three hundred twenty-two cases of cervical dysplasia (mild, moderate, and severe) and carcinoma in situ (CIS) were examined for the presence of papillomavirus structural antigens with a peroxidase-antiperoxidase method on formalin-fixed, paraffin-embedded tissue. The primary antiserum, prepared from purified, detergent-disrupted bovine papillomavirus type 1 virions, is broadly reactive against the genus-specific (common) antigen(s) of the papillomaviruses. Using the peroxidase-antiperoxidase technique on cervical tissue obtained from biopsy, conization and hysterectomy specimens, papillomavirus structural proteins were identified in association with mild dysplasia in 65 of 152 (43%) cases, with moderate dysplasia in 12 of 82 (15%) cases, with severe dysplasia in eight of 47 (17%) cases, and with CIS in four of 41 (10%) cases. Papillomavirus antigens were found directly within the lesion in all the cases of mild and moderate dysplasia but in only two instances of severe dysplasia and in none of the examples of CIS. In the remaining 10 cases of severe dysplasia and CIS associated with the presence of papillomavirus antigens, cells containing papillomavirus structural proteins were present in areas of moderate dysplasia immediately adjacent to the high-grade lesions in seven instances and in areas of mild or moderate dysplasia not directly in contact with the high-grade lesions in three. Among the 12 high-grade lesions associated with the presence of papillomavirus antigens, a morphologic transition from areas of moderate dysplasia containing papillomavirus antigens to the areas of severe dysplasia and CIS was present in five instances. The results of this study, therefore, provide direct evidence demonstrating the relationship of papillomavirus to intraepithelial cervical neoplasia ranging from mild dysplasia to severe dysplasia and CIS.