1. 1. In Rana esculenta L. secretion of gastric juice was evoked by mechanical stimulation of the stomach. The output of gastric juice depends on the strength and the duration of the mechanical stimulus. 2. 2. “Spontaneous” secretion was found to be negligible compared with mechanically induced secretion. 3. 3. Frogs in which the stomachal branch of the splanchnic nerve was cut showed a normal secretory response to the mechanical stimulus. Double vagotomy did not abolish the secretory response of the stomach to mechanical stimulation, although the pepsin secretion was reduced by vagotomy to approximately 60 per cent of the original. 4. 4. No secretion via a reflex in the sympathetic system could be demonstrated in Rana. An indirect sympathetic influence, however, did exist, for sympathetically induced vasoconstriction led to a lowering of the secretory output. 5. 5. Destruction of the C.N.S. resulted in a strong reduction of the secretory output. This reduction is supposedly caused by the greatly reduced blood-supply which results from destruction of the C.N.S. and by loss of blood. 6. 6. Administration of ergotamine and hexamethonium chloride did not change the secretory response significantly. Injection of atropine sulphate led to inhibition of secretion; this occurred also in frogs in which the stomach was partly or totally deprived of its extrinsic nerve supply. The secretory response to the mechanical stimulus is under the control of cholinergic fibres of the intramural nerve plexus. 7. 7. The rate of blood-flow of the oesophagus and the stomach influences the secretion of pepsin. Vasoconstriction in the splanchnic area leads to a lowering of the secretory output. In frogs which were exercised the secretion was strongly inhibited, this probably being due to a high adrenosympathetic tone. 8. 8. Subcutaneous administration of histamine caused some increase in pepsin output. This increase was not caused by flushing of preformed enzyme, but by active secretion of pepsin.