Routinely processed paraffin sections from 20 patients with adult laryngeal papillomas were examined for the presence of human papillomavirus type 11 (HPV-11) DNA and its specific mRNA by in situ hybridization methods using 35S-labeled RNA probes. Immunohistochemical techniques were also used to identify papillomavirus genus-specific common antigen (pgs-antigen). HPV-11 DNA signals and/or papillomavirus genus-specific common antigen were detected in all eight samples of multiple laryngeal papilloma. On the other hand, in 12 samples of single laryngeal papilloma, neither papillomavirus genus-specific common antigen nor HPV-11 DNA were detected. Four patients were positive for both HPV-11 DNA and pgs-antigen. In three of these four patients, HPV-11 mRNA signals were also detected. These results provided direct evidence of the association of HPV and adult multiple laryngeal papilloma.