A recommendation has been made by the CDC that HIV positive individuals not be considered for organ transplantation. One reason for this recommendation is the thought that post-transplant immunosuppression would cause exacerbation of HIV induced disease. Recent studies performed at the Tulane Primate Center and elsewhere demonstrate that treatment with cyclosporin A, prednisone, and total lymphoid irradiation do not exacerbate and may decrease the severity of simian immunodeficiency virus (SIV) infection in rhesus monkeys. We performed a short term (30 day) dosing experiment in 9 SIV-infected rhesus monkeys using mycophenolate mofetil (MMF), an immunosuppressive drug used in human organ transplant recipients. Twice daily oral MMF treatment was initiated 5 months after animals were inoculated with SIV Delta B670 rhII. White blood cell counts, hematocrit, body weight and platelet counts remained within normal limits during the 30 day treatment period. Physical examination findings remained constant throughout the study. QC-PCR revealed no significant change in viral copy numbers in plasma. These preliminary data suggest that at the dose, frequency and duration of MMF used in this study at 5 months post inoculation, SIV disease was not exacerbated.