In a prospective study, 355 healthy, asymptomatic, male volunteers, 18 to 45 years of age, were screened by esophagogastroduodenoscopy before admission to clinical trials. One hundred thirty-four volunteers (38%) showed abnormal endoscopic findings. Some volunteers had more than one site of involvement or more than one grade of lesion in each anatomic location. In 49 (14%) of these subjects the esophagus was a site of involvement, while in 86 (24%) the stomach was involved, and in 71 (20%) the duodenum was involved. The point prevalences in these asymptomatic subjects were 8.5% for erosive esophagitis, 12% for erosive gastritis, 10% for erosive duodenitis, 2% for gastric ulcer, and 2% for duodenal ulcer.