Human papillomaviruses (HPV) have been implicated in the pathogenesis of human squamous cell carcinoma, specially of cervical carcinomas. In previous studies concerning primary lung cancer, DNA of HPV subtypes was detected by in situ hybridization or polymerase chain reaction (PCR), up to 30% of the cases, namely in squamous cell carcinomas. A series of 31 frozen biopsies of lung carcinomas (surgical biopsies or through fiber optic bronchoscopy) were examined for the presence of HPV DNA by nested PCR. Primers for the two steps were type-specific primers (6/11-16 and 18; kit Amplicis-HPV) for the transforming region of HPV. HPV-DNA was found in five tumors: in two of 18 cases of squamous cell carcinoma (11%), in one of four cases of adenocarcinoma, in one of six cases of small cell carcinomas and in the unic case of neuro-endocrin carcinoma. No case of the two large cell undifferentiated carcinomas was positive. There were three cases of HPV 6/11, one case of HPV 16, and one sample positive for HPV 6/11 and HPV 18. No morphologic changes consistent with HPV lesions were observed. The frequency of 11% among the squamous cell carcinomas is near those found by previous studies (9 to 20% for HPV 6-11-16-18). For the first time, HPVs have been detected in neuro-endocrin tumors, and this have to be confirmed by studies of many more cases. So HPV might play a role as promoter in carcinogenesis of any types of lung carcinoma, although at a low frequency.