1. J. M. Chan and M. J. Stampfer, Department of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115, USA.
2. E. Giovannucci and J. Ma, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
3. P. H. Gann, Department of Preventive Medicine, Northwestern University Medical School, Chicago, IL 60611, USA.
4. P. Wilkinson and M. Pollak, Cancer Prevention Research Unit, Departments of Medicine and Oncology, Lady Davis Research Institute of the Jewish General Hospital and McGill University, Montreal, Canada H3T1E2.
5. C. H. Hennekens, Division of Preventive Medicine, Department of Medicine and Department of Ambulatory Care and Prevention, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.