Argyrophil cell (AC) hyperplasia in corpus mucosa was investigated in 53 patients with chronic gastric ulcer disease not previously treated with antisecretory drugs. Mucosal biopsies were taken stepwise from the posterior wall in the corpus area of the stomach. Of 117 biopsy sites, 28 showed gastritis without atrophy, 85 showed chronic atrophic gastritis of varying degrees while 4 biopsies showed a normal mucosa. About one third (38%) showed a normal AC pattern. Of the remaining two thirds (62%), 45% had simple AC hyperplasia, 18% had linear and 37% had micronodular AC hyperplasia. A strong association was found between focal (linear/micronodular) AC hyperplasia and chronic atrophic gastritis. It is concluded that focal AC hyperplasia is a common phenomenon in gastric ulcer patients and is inherently related to the spontaneous development of atrophy in the corpus mucosa of these patients.