1. From the Department of Pediatrics, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill. N.C., and the Clinical Biochemistry Laboratory, Division of Nutrition and Endocrinology, American Health Foundation. Valhalla, N.Y. Address reprint requests to Dr. Greenberg at the Department of Pediatrics, Burnett-Womack Building 229H, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27514.