The activities of the specific histidine decarboxylase (EC 4.1.1.22) and dopa decarboxylase (EC 4.1.1.26) were determined radiometrically in the glandular portion of the stomach of 250 female rats in restraint stress induced by immobilisation at 2-hour intervals during a period of 2–30 h. After 3 h the histidine decarboxylase showed a continuous increase in activity and attained a maximum of more than twice the activity in the control animals between 9 and 11 h, respectively. The dopa decarboxylase activity was only moderately raised until 11–13 h after the beginning of immobilisation and revealed twice the activity after 13–15 h. Subsequently, the activity of both amino acid decarboxylases decreased and dropped to below the normal level after 21 h. The induction mechanisms and the significance of the increased amounts of histamine and dopamine formed for the vasculature of the gastric mucosa and for the development of erosions are discussed.