With increasing survival rates of children grafted for different malignancies concerns about the longterm side effects of this treatment are growing. Therefore, investigations on the function of endocrine systems were conducted in a total 28 patients grafted for various reasons: ALL (N = 18), AML (N = 1), SAA (N = 3), CML(N = 4), neuroblastoma (N = 2). The results can be summarized as follows: 1. The extent of hormonal derangements is primarily dependent on the extent of irradiation prior to BMT. Integrity of hormonal systems was found in cases without irradiation (SAA) or if TBI did not exceed 3 Gy. 2. Primary hypogonadism was present in 18 patients. 3. Primary hypothyroidism was present in 2 patients. 4. Growth impairment was observed in 8 patients. In four of these cases growth hormone deficiency was the cause. In four other cases with graft-versus-host-disease and hepatic involvement SmC/IGF I levels were severely diminished. The data suggest that in most cases BMT itself has relatively few negative effects on the endocrine regulatory system. However, more detailed investigations before and after BMT will be needed to further validate these observations.