Studies on the involvement of the human papillomavirus (HPV) in initiation and progression of oral neoplasia have generated conflicting results. The observed discrepancy is attributable mainly to the varying sensitivity of the applied methodologies and to epidemiologic factors of the examined patient groups. To evaluate the role of HPV in oral carcinogenesis, we analyzed 53 potentially neoplastic and neoplastic oral lesions consisting of 29 cases of hyperplasia, 5 cases of dysplasia, and 19 cases of squamous cell carcinomas, as well as 16 oral specimens derived from healthy individuals. A highly sensitive nested polymerase chain reaction (PCR) assay was used, along with type-specific PCR, restriction fragment length polymorphism analysis, dot blotting, and nonisotopic in situ hybridization. Nested PCR revealed the presence of HPV DNA in 48 of the 53 (91%) pathologic samples analyzed, whereas none (0%) of the normal specimens was found to be infected. Positivity for HPV was independent of histology and the smoking habits of the analyzed group of patients. At least one "high risk" type, such as HPV 16, 18, and 33, was detected by type-specific PCR in 47 (98%) infected specimens, whereas only 1 (2%) squamous cell carcinoma was solely infected by a "low risk" type (HPV 6). HPV 16 was the prevailing viral type, being present in 71% of infected cases. Single HPV 16 and HPV 18 infections were confirmed by restriction fragment length polymorphism. HPV 58 was detected by dot blotting in three hyperplastic lesions. HPV positivity and genotyping were further confirmed, and the physical status of this virus was evaluated by nonisotopic in situ hybridization. Diffuse and punctate signals, indicative of the episomal and integrative pattern of HPV infection, were observed for low- and high-risk types, respectively. Our findings are suggestive of an early involvement of high-risk HPV types in oral carcinogenesis.