Based on observations of primary Sjögren's syndrome (SS) following acute Epstein-Barr virus (EBV) infection, the authors hypothesized that EBV may play a role in the pathogenesis of SS. This hypothesis was tested by evaluating ten peripheral blood mononuclear (PBMN) cell specimens, ten lacrimal gland biopsies, and five tear specimens from 15 EBV-seropositive primary SS patients for EBV genomic sequences using polymerase chain reaction (PCR). Epstein-Barr virus DNA sequences were detected in 50% of SS PBMN cell specimens and 80% of SS lacrimal gland and tear specimens. In six SS patients, specimens were obtained from two or more sites (i.e., PBMN cell and lacrimal gland and/or tears), and EBV genomic sequences were amplified in the PBMN cells and the lacrimal gland or tears in three of these subjects. The authors previously detected EBV genomes in 32% (11/34) of normal human lacrimal glands from EBV-seropositive donors using PCR and concluded that the normal human lacrimal gland may be a site of EBV persistence; however, they were unable to amplify EBV sequences in DNA from PBMN cells or tear specimens from normal donors. Amplification of EBV DNA in PBMN cells, lacrimal glands, and tears of primary SS patients at a greater frequency (P less than 0.01) than normal controls suggests that EBV may be a risk factor in the pathogenesis of SS.