The mechanism of action of an extract of intestinal mucosa that accelerates the disposal of glucose given intravenously in normal man was investigated. The active material is biologically distinguishable from pancreozymin, and its effects cannot be attributed to insulin, insulin-like activity, glucagon or amino acids in the preparation. The extract enhances the increase in blood-insulin concentration which occurs in response to the intravenous infusion of glucose in normal man and which has been compared with that following ingestion of glucose. No response was demonstrable in insulin-treated juvenile-onset diabetes, and it is suggested that the extract acts in normal subjects by stimulating the jrelease of endogenous insulin. It is concluded that an insujln-aecretagogue, derived from the small intestine, may be concerned in the response to ingested glucose, and that such, an agent may be present in the active extract.