1. National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina.
2. Present address: Millennium Pharmaceuticals, Inc., Cambridge, Massachusetts.
3. Integrated Laboratory Systems, Research Triangle Park, North Carolina.
4. Present address: Family Health International, Research Triangle Park, North Carolina.
5. Present address: Novartis Institutes for Biomedical Research, Cambridge, Massachusetts.
6. University of North Carolina, Chapel Hill, North Carolina.
7. Present address: Brigham and Women's Hospital, Boston, Massachusetts.
8. National Cancer Institute, Bethesda, Maryland.