Epstein Barr virus (EBV) infection has been associated with the post-transplant lymphoproliferative disorder (PTLD) in up to 8% of transplant recipients. Primary EBV infection and the use of antilymphocyte preparations appear to increase the incidence of PTLD. Experimental evidence suggests that the antiviral prophylaxis used by many transplant programs may influence the development of this post-transplant complication. In order to investigate the influence of antiviral prophylaxis (intravenous ganciclovir followed by high-dose oral acyclovir) on the development of PTLD in kidney-pancreas and liver allograft recipients from the University of Washington Medical Center, records were reviewed for pretransplant EBV status, antilymphocyte preparation use and for histologic documentation of PTLD. Two of 83 kidney-pancreas recipients (1 EBV-seronegative, 1 EBV-seropositive) and 1 of 123 liver recipients (EBV-seropositive) has developed PTLD. Six of 83 kidney-pancreas patients were EBV-seronegative prior to transplantation and 4 of these patients received at least two courses of an antilymphocyte preparation. Thirty-eight (49%) of the 77 EBV-seropositive kidney-pancreas recipients received at least two courses of an antilymphocyte globulin without the development of PTLD. Both the EBV-seronegative kidney-pancreas and the liver recipient who developed PTLD had received multiple courses of antilymphocyte globulins. One EBV-seropositive kidney-pancreas recipient had only received one course of OKT3 1 year prior to the development of PTLD. The incidence of PTLD reported here in patients receiving intravenous ganciclovir followed by high-dose oral acyclovir antiviral prophylaxis is lower than previously recorded when consideration is given for patient's EBV status and the use of antilymphocyte preparations.