1Gastroenterology Service, Hospital de LeĂłn, LeĂłn, Spain
2Gastroenterology Service, ClĂnica Puerta de Hierro, Madrid, Spain
Reprint requests and correspondence: Santiago Vivas, MD, Gastroenterology Service, Hospital de LeĂłn, Altos de Nava s/n, 24008 LeĂłn, Spain.
Received 27 December 1999; accepted 29 December 1999