These data demonstrate that endocrine function abnormalities influencing subsequent growth and development in children after marrow transplantation rarely occur after preparation with CY alone. However, after administration of regimens containing TBI, multiple endocrine function abnormalities can occur. Although longer follow-up is needed, it appears that the addition of BU to CY does not result in thyroid function or growth abnormalities. Pubertal development and gonadal function, however, may be adversely influenced by BU and patients may require supplementation with appropriate gonadal hormones.