Paraffin sections of 11 undifferentiated salivary gland carcinomas of lymphoepithelioma type (malignant lymphoepithelial lesion) arising in Greenlandic Eskimos (Inuit) were examined for the presence of Epstein-Barr virus (EBV) using in situ nucleic acid hybridization with a 35S-labeled EBV-specific probe. Epstein-Barr virus genomes were detected in each case in malignant epithelial cells, but were not found in lymphoid stroma or in residual benign salivary epithelium. Eight undifferentiated salivary gland carcinomas from non-Eskimo patients (including two with lymphoepithelioma-like features) were negative for EBV-DNA. Our results confirm the existence of a consistent and specific association between EBV and tumor cells of undifferentiated salivary gland carcinoma of lymphoepithelioma type arising in Greenlandic Eskimos.