A roundtable meeting to discuss the use of therapeutic drug monitoring (TDM) to guide immunosuppression with mycophenolate mofetil was held in New York in December 2004. Existing recommendations for the initial months after transplantation were updated. After ensuring adequate levels of mycophenolic acid (MPA, the active metabolite of mycophenolate mofetil) immediately after transplantation, optimal efficacy may require only a few dose adjustments, because intrapatient variability in exposure seems low. Recommendations based on current knowledge were made for posttransplantation sampling time points and for target MPA concentrations. Algorithms for estimating MPA exposure using limited sampling strategies were presented, and a new assay for MPA discussed. It was agreed that because of interpatient variability and the influence of concomitant immunosuppressants, TDM might help optimize outcomes, especially in patients at higher risk of rejection. The value of TDM in the general transplant population will be assessed from large, ongoing, randomized studies.