The Epstein-Barr virus is associated with a broad spectrum of lymphoproliferative diseases in liver allograft recipients. To investigate the effects of primary infection in children following liver transplantation and the possible role of Epstein-Barr virus in the pathogenesis of unexplained chronic hepatitis after transplantation, we used an in situ hybridization technique to detect small virus encoded nuclear RNAs in posttransplant specimens. For comparison, other posttransplant complications and diseases occurring in the nontransplanted liver were studied with the same method. We examined 114 specimens in the following categories: (a) children with primary Epstein-Barr virus infection after transplant (n = 25), (b) chronic hepatitis more than 12 mo after transplant (n = 14), (c) rejection (n = 15), (d) normahear-normal histology more than 12 mo after transplant (n = 13) (e) end-stage acute liver disease (n = 9) and (f) end-stage cirrhosis (n = 38). Thirty-three of 114 specimens had labeling of occasional portal and parenchymal lymphoid cells. These were present in each of the six main diagnostic categories listed above: 2 of 25, pediatric; 6 of 14, chronic hepatitis; 4 of 15, rejection; 1 of 13, normal; 4 of 9, acute; and 16 of 38, cirrhosis. In none of the patients with Epstein-Barr virus-infected cells did lymphoproliferative disease subsequently develop. In conclusion, we have been unable to show an obvious association between Epstein-Barr virus infection and graft dysfunction after liver transplantation. Our results suggest that immunological response to primary infection in children after liver transplantation may be adequate. Small numbers of Epstein-Barr virus-infected cells are present in a wide range of liver diseases. The finding of occasional infected cells in posttransplant biopsy tissue does not predict progression to lymphoproliferative disease. (HEPATOLOGY 1994;20:899–907).