Sera from patients with nasopharyngeal carcinoma (NPC) or other malignant diseases and from apparently healthy controls were examined for Epstein-Barr virus (EBV) antibodies. A difference existed in the percentage of positive sera among the groups studied. High-titer antibody levels were observed in the NPC group, but no statistical difference was found among other groups of patients and controls. The data reaffirmed the association of EBV with NPC but did not support its etiologic role in the development of other human neoplasms.