1. Division of Chemical Pathology, Centre for Mechanisms of Human Toxicity, PO Box 138, University of Leicester, Lancaster Rd., Leicester, LE1 9HN
2. Department of Mutagenesis, ICRF Clare Hall Laboratories, Blanche Lane, South Mimms, Potter's Bar, EN6 3LD
3. Department of Medicine, The Medical College of St. Bartholomew's Hospital, West Smithfield, London, EC1A 7BE