Five hundred and thirteen cases of gastric carcinoma were investigated for the presence of viral RNA, and the clinico-pathological data, geno-type, BamHIF restriction fragment polymorphism (RFLP) and specific LMP-1 30 bp gene deletion were also examined. EBVs detected in lymphocytes in 20 normal gastric mucosa, 7 lymphoma cell lines (LCLs) maintained in severe combined immunodeficiency (SCID) mice and 18 non-Hodgkin's lymphomas were compared with those in the gastric carcinoma cases. Thirty-three cases (6.4%) were demonstrated to be positive for EBV by means of EBER-1 RNA in situ hybridization. Clinico-pathological data showed no statistically significant difference in histological grading, location of cancer and status of vessel and lymphatic invasion between the EBV-positive and -negative groups, although the former significantly predominated in the submucosal invasion group (submucosal vs mucosal P=0.021; submucosal vs advanced cancer P=0.033). Some of these data were different from corresponding data in earlier reports. In cases that were evaluated by molecular biology, type A, wild-type F and LMP-1 gene deletion predominated except one in 21 informative cases, one in 24 and two in 16, respectively. EBVs detected in lymphocytes in normal gastric mucosa, LCLs in SCID mice and non-Hodgkin's lymphoma were also predominantly affected by type A, wild-type F and LMP-1 gene deletion with few exceptions. The results indicate a lack of genetic differences among EBVs in gastric carcinoma, normal population, LCLs of SCID mice and non-Hodgkin lymphomas. Some EBV infections in gastric carcinomas may be transient, especially in the submucosal invasion group.