The human papilloma virus (HPV) associated with hyperplastic epithelium in an oral denture fibroma was examined by southern blot hybridization. Extracted DNA was hybridized with full length linear HPV type 2a, 6b, 11, 16, 18, 31 and 33 DNAs as a mixed probe only under low stringent conditions. The hybridized bands digested with Bam HI and Eco RI were approximately 8.8 kbp and 15 kbp, respectively. Thus the lesional HPV DNA was different from HPV types used as probes and was probably integrated into host cell chromosomal DNA judging by the off-size high molecular weight bands. Considering the contaminating mesenchymal region and uninfected epithelial cells as well as the evidently limited homology with probe HPV DNAs, the virus copy number in infected cells was poorly defined. In situ antigen staining signals were widely detected in the hyperplastic epithelial layer.