Histological sections from paraffin-embedded breast carcinoma and axillary lymph nodes were examined for the presence of human papillomaviruses by two different techniques: the polymerase chain reaction (PCR) and the in situ hybridization with biotin-labelled probes. By PCR we detected HPV 16 DNA sequences in 29.4% of breast tumours and in some metastatic lymph nodes, though we were unable to identify any HPV DNA sequences by in situ hybridization. These results suggest that HPV's could play a role in the genesis of breast neoplasia.