Mammalian target of rapamycin inhibitors have the potential to make a further impact in two areas. The first and most immediate possibility is through a reduction in the incidence and severity of allograft vasculopathy, with particular emphasis on heart allograft recipients. Finally, these inhibitors are poised to make major contributions when costimulation blockade agents eventually make their way to the clinic and as experimental tolerance induction, protocols become more widely applied. © 2004 Lippincott Williams & Wilkins.