Harris, I.L.; Smith, M.F.; Harris, I.L., Z/Yen Limited 5-7 St Helen's Place London EC3A 6AU, UK Tel: 0171 562 9562 Fax: 0171 628 5751 Email: zyenilh@zyenharri.win-uk.net; Smith, M.F., Department of General Practice and Primary Care St Bartholomew's and the Royal London School of Medicine and Dentistry Queen Mary and Westfield College University of London Tel/Fax: 0171 582 1409 Email: m.smith@qmwac.uk