Sixty-seven patients with Barrett's esophagus have been prospectively followed over an average of 36 months (range 6 to 76 months) with standardized endoscopic observation and biopsies of the length of columnar epithelium. The initial length of Barrett's epithelium ranged from 1 to 16 cm, mean 5.5 cm. Specialized columnar epithelium was present in 64 of the 67 patients. Patients were treated predominantly with H2-receptor blocker therapy to relieve symptoms. Eighty-two percent of patients had less than a 1-cm change in length per year. The mean rate of change of length was -0.093 cm per year. These results confirm in a relatively large, prospective study that standard antireflux therapy for Barrett's esophagus does not result in consistent reduction in the extent of Barrett's epithelium over a three-year interval.