Gastrointestinal complaints, including peptic ulcer, are believed to be associated and enhanced by shift work (SW). However, there are no clear reports in the literature about this acquired pathology. Serum gastrin (G) and group I pepsinogen (PG1) are thought to play a role in the pathogenesis of peptic ulcer and may be considered a useful test of the gastric function. Five adult male foundry shift workers, without any demonstrated gastrointestinal pathology, were studied over a month's span during the following weekly rotating shift schedule: 07.45-16.45, 06.00-14.00, 14.00-22.00, 22.00-06.00. Six adult, day-working males acted as controls. Blood samples drawn at the beginning and at the end of each weekly shift were assayed for G and PG1 utilizing RIA kits. Our data showed that SW causes a prominent change in the gastrin/acidopepsin secretion system.