The General Clinical Research Center provides discrete hospitalization facilities for careful research investigation of volunteer human subjects admitted on defined, previously approved protocols. At the present time major emphasis has been on the program in renal transplantation in which a multi-disciplinary approach has been used to define certain renal aspects of erythropoiesis, digoxin metabolism and distribution, blood pressure regulation, and aldosterone metabolism. Collaborative efforts in tissue typing and immunologic aspects of transplantation immunity are being carried out with other Medical Centers. Immunosuppressive therapy of scleroderma and nephrotic syndrome are being evaluated. Other active protocols include studies pertaining to the mechanism of cold-diuresis, investigation of the metabolic effects of human growth hormone, and evaluation of creatine metabolism in various neuromuscular disorders.