Prior retrospective studies have suggested that tacrolimus monotherapy is an option associated with excellent outcomes and reduced toxicities.We conducted a prospective, randomized, 2-center study of tacrolimus combination therapy vs monotherapy. From April 16, 2004, to September 15, 2005, 58 adult heart transplant patients were studied. All received oral tacrolimus, mycophenolate mofetil, and corticosteroids. Patients were then randomized to a group where mycophenolate was maintained (COMBO) or to a group where it was discontinued (MONO) 14 days post-transplant. Corticosteroids were rapidly withdrawn in both groups between 8 and 12 weeks.The primary end point (mean 6-month International Society of Heart and Lung Transplantation biopsy score) was 0.44 +/- 0.04 in the MONO group and 0.60 +/- 0.05 in the COMBO group (p = 0.013, unpaired Student's t-test). The freedom from rejection grade of 2R or higher at 6 and 12 months was 93.3% with MONO and 92.9% with COMBO (p = NS).Tacrolimus monotherapy appears to be safe and efficacious in heart transplant recipients and is not associated with excess rejection in the first year post-transplant. Further studies of this approach are warranted.