Thirty nine papillomas and 14 precancerous lesions, from skin and mucosa were studied for the presence of human papillomavirus (HPV) infection on frozen sections or on paraffin embedded sections by comparison of 2 methods: (1) Detection of group specific viral antigen by immunohistochemical techniques with a rabbit antiserum raised to highly purified virus dissociated by SDS (sodium dodecylsulfate) and heating: (2) detection of viral DNA by an in situ molecular hybridization technique with biotinylated probes. In non-stringent conditions of hybridization (20 p. 100 formamide, Tm = -33 degrees C) viral DNA sequences were more frequently detected (85%) than viral antigen (32%). They were detected in a high proportion of cutaneous and mucosal papillomas as well as in precancerous lesions. They were found in 7 out of 8 biopsies from Bowen's disease and bowenoid papulosis, which were viral antigen negative. Under stringent conditions (50 p. 100 formamide, Tm = -12 degrees C) in situ hybridization allowed typing of HPV. Identical results were obtained in most lesions using in situ hybridization and the Southern technique. Some discrepancies were observed in mucosal lesions, which could be due to the presence or absence of infected foci in the different fragments. Thus, with in situ hybridization it is possible to evaluate the risk of evolution towards malignancy when potentially oncogenic types are present in the biopsies. In the absence of viral DNA in lesions, complementary methods should be used (detection of viral DNA with Southern technique or detection of RNA transcripts).