Dr. Graham R. Taylor is Scientific Director of the Yorkshire Regional DNA Laboratory and Technical Director of the ICRF core mutation detection facility. He also holds an appointment as senior associate lecturer at the Leeds University School of Medicine. He is organizer of the mutation detection training course program run by the Human Genome Organization. Dr. Ian N. M. Day is Lister Institute Professor and Head of the Department of Human Genetics and Director of the Human Genetics Research Division at the University of Southampton.