Summary Hydrocortisone (50 mg intramuscularly daily) was given to 3 dogs with Heidenhain pouches for a period of 37 days. Maximal acid and pepsin output in response to histamine and gastrin increased during hydrocortisone administration. During control studies, the mean maximal acid output in response to gastrin was lower than to histamine but the maximal responses to these 2 stimulants were generally equal during hydro-cortisone administration. In contrast, mean maximal pepsin output was higher with gastrin during control studies and remained higher than histamine during administration of hydrocortisone.