Paraffin embedded archival tissue from 7/49 carcinomas of the lung which were positive for HPV DNA examined by multiple PCR were again searched for HPV DNA by in situ hybridization technique. Five cases were found positive for HPV DNA by in situ hybridization, of which three cases were positive for HPV 11, One was positive for HPV 16 and the other was positive for both HPV 11 and 16. The hybridization signal was mainly located in the nuclei of the koilocytotic tumor cells. These results suggest that HPV infection may have some role in the development of squamous cell carcinoma of the lung.