This prospective randomized study compared the effects in heart transplant recipients of thymoglobulin and ATG, two rabbit polyclonal antithymocyte antibodies available for induction therapy. Among 40 patients (29 men and 11 women, mean age: 40.7 +/- 14 years) undergoing orthotopic heart transplantation, 20 were randomly allocated to receive induction with thymoglobulin (group A) and 20 to ATG-fresenius (group B). Comparisons between the two groups included early posttransplant (6 months) incidence of acute rejection episodes (grade >/= 1B), bouts of steroid-resistant rejection, time to first rejection, survival, graft atherosclerosis, infections, and malignancies. The study groups displayed similar preoperative and demographic variables. No significant difference was found with regard to actuarial survival (P =.98), freedom from rejection (P =.68), number of early rejections > 1B (P =.67), mean time to first early cardiac rejection (P =.13), number of steroid-resistant rejections (P =.69). Cytomegalovirus reactivations were more frequent among group A (65%) than group B (30%; P =.028). New infections due to cytomegalovirus occurred only in group A (four patients; 20%; P =.05). No cases of malignancies were observed at a mean follow-up of 32.8 +/- 8.9 months. Although thymoglobulin and ATG showed equivalent efficacy for rejection prevention, they have different immunological properties. In particular, thymoglobulin seems to be associated with a significantly higher incidence of cytomegalovirus disease/reactivation.