We studied the incidence of GBV-C infection in patients with oral cancer or oral lichen planus (OLP). Subjects included 38 patients with oral cancer and 34 patients with OLP from whom serum was collected to detect GBV-C-RNA using reverse transcription (RT) "nested" PCR. GBV-C-RNA was positive in 1 (2.6%) oral cancer patient and 3 (8.8%) OLP patients. All 4 GBV-C-positive patients were also positive both for the antibody for hepatitis C virus (anti-HCV) and HCV-RNA, indicating simultaneous infection with GBV-C and HCV. In conclusion, GBV-C infection was found in 5.5% (4/72) of oral cancer or OLP patients and all patients infected with GBV-C also had HCV infection. This suggests that GBV-C infection is unlikely to play an important role in the pathogenesis of oral cancer and OLP.