New research into the understanding of the biology of hepatitis C and B viruses, including their genotypic diversity, is providing insights into their pathogenicity after organ transplantation. Effective treatment, however, remains a challenge. Tests for rapid and reliable detection of cytomegalovirus are continuing to evolve and have important implications for effective management of cytomegalovirus after transplantation. The unusual manifestation (smooth muscle tumors) of a common virus (Epstein-Barr virus) after transplantation has been described. Finally, the new immunosuppressive agent tacrolimus may reduce the number of infections after organ transplantation.