| 2006 – Present | Adjunct Professor of Genetics and Pathology, University of Utah |
| 2006 – Present | Division of Hematology and Hematologic Malignancies, Department of Internal Medicine, University of Utah |
| 2006 – 2020 | Director, Hemoglobin and Molecular Genetics, ARUP and University of Utah |
| 2001 – 2006 | Director, Baylor Red Cell Reference Laboratory |
| 2001 – 2006 | Professor of Pediatrics, Baylor College of Medicine |
| 2000 – 2006 | Professor of Medicine and Cell Biology, Baylor College of Medicine |
| 2000 | Chair, American Society of Hematology Committee for Eastern Europe |
| 1994 – 2000 | Director UAB NIH Designated Sickle Cell Center, Univ. of Alabama |
| 1986 – 2000 | Professor of Medicine/Hematology, Univ. of Alabama at Birmingham |
| 1987 – 2000 | Professor of Biochem/Mol. Genetics, Univ. of Alabama at Birmingham |
| 1984 – 1985 | Visiting Assoc. Professor, UCSF & the Howard Hughes Institute |
| 1979 – 1985 | Associate Professor of Medicine/Hematology, Univ. of Alabama at Birmingham |
| 1976 – 1979 | Assistant Professor of Medicine/Hematology, Univ. of Alabama at Birmingham |