To observe the distribution of Epstein-Barr virus (EBV) in pulmonary carcinoma, 87 cases of pulmonary carcinoma were used to detect EBV infection by in situ hybridization. The positive rate of EBV infection in carcinoma tissue and peripheral lung tissue were 37.9% (33/87) and 11.5% (10/87) respectively. The existence of EBV was related to both the degree of carcinoma differentiation and lymphocyte infiltration. The EBV positive rates and hybridization signals in the groups of moderately and poorly differentiated carcinoma were significantly higher and stronger than those in the group of well differentiated carcinoma. The degree of lymphocyte infiltration increased with the increase of EBV positive rate. These results indicate that there is a relationship between EBV infection and the biological features of cancer, and that EBV may play a role in the pathogenesis of pulmonary carcinoma.