To determine the prevalence of genetic polymorphisms in Epstein-Barr virus (EBV) strains in the Korean population, the restriction site polymorphisms for BamHI and XhoI enzymes were analyzed with 16 EBV isolates from cancer patients and 7 EBV isolates from healthy carriers, using polymerase chain reaction techniques. None of the 23 isolates were found to carry an extra BamHI site in the BamHI F-fragment (f-variant). Of the 12 type-1 isolates from the cancer patients, 10 lost both the LMP1 XhoI site and the BamHI site between the BamHi W1* and I1* fragments (a W1*I1* fusion variant or type C). The latter W1*I1* fusion variant was due to a mutation of thymidine to adenine, as evidenced by a sequence analysis. The remaining two type-1 isolates showed either no variation at both sites or the loss of only the XhoI site. In contrast, two type-2 isolates and two intertypic recombinants with a type-1 allele at the EBNA2 locus and type-2 alleles at all or some of the EBNA3 loci retained both enzyme sites. In similar analyses of the 7 isolates from the healthy carriers, five of six type-1 isolates lost these two sites, however, one type-2 isolate did not. These results clearly indicate a strong association of both the LMP1 XhoI site loss and the W1*I1* fusion variant with the type-1 rather than the type-2 EBV strains circulating in the immunocompetent Korean carriers.