Mycophenolate mofetil (MMF) has been approved as an immunosuppressive agent in kidney transplant recipients and may thus be used concomitantly with antiherpetic agents, the latter for the treatment of intercurrent herpesvirus infections. The parent compound of MMF, mycophenolic acid (MPA), is a potent inhibitor of inosine monophosphate dehydrogenase and causes depletion of the intracellular (deoxy)guanosine triphosphate [(d)GTP] pools. Lobucavir [1R(1alpha,2beta,3alpha)]-9-[2,3-bis(hydroxymethyl)cyc lobutyl]guanine (LBV) is a novel antiviral agent with activity against ganciclovir-resistant cytomegalovirus (CMV) strains, that is in phase II clinical trials for the treatment of CMV infections. LBV triphosphate inhibits the viral DNA polymerase competitively with dGTP. We present the results of our studies on the antiviral effects of the combinations LBV + MMF and LBV + MPA.