GI Fellowship: University of Colorado Medical Center, Department of Gastroenterology, Denver, CO, 1974-1976. 1976-1978: Expert, National Institutes of Health, National Cancer Institute and National Institute of Arthritis, Metabolism, and Digestive Diseases, Digestive Diseases Branch. 1979-1987: Senior Investigator, National Institutes of Health, National Institute of Arthritis, Diabetes and Digestive and Kidney Diseases, Digestive Diseases Branch. 1988-1991: Chief, Section on Cell Biology, Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, United States Public Health Service (0.6). 1991-2000: Chief, Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, Chief, Section on Gastroenterology, National Institutes of Health, United States Public Health Service (0.6). 2001-2004: Chief, Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases; Chief, Section on Gastroenterology, National Institutes of Health, Civil Service-Title 42. 2004-Present: Chief, Cell Biology Section, Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Civil Service-Title 42.