A primary goal in organ transplantation is the prevention or effective treatment of infection, the most common life-threatening complication of long-term immunosuppressive therapy. The challenges involved in achieving this goal are several: a broad range of potential sources of infection ranging from latent viruses to pathogens of both community and hospital origin; immunosuppression-induced impairment of the inflammatory response, which attenuates the signs and symptoms of invasive infection; and the adverse effects of the antimicrobial drugs used for prophylaxis and therapy, which result both from the duration of therapy required and from interactions with the immunosuppressive drugs cyclosporine and tacrolimus. Our . . .