Gastric mucous secretions were collected in fasting patients following a careful gastric washout. The stomach, perfused with saline, was continuously reaspirated. Saliva was obtained separately during the test. Gastric and salivary secretions were collected in four successive 30-min samples. Saline was infused intravenously, alone during the first control period, associated to various doses of secretin during the three following periods: 0 U/kg/h (control series); 0.125 U/kg/h (series II); 0.395 U/kg/h (series III); 1.250 U/kg/h (series IV). The highest dose of secretin induces a sustained increase in the output of fucose, galactose, total hexosamines, uronic acids and sulfate. The variation in the output of mucosubstances aspirated from the human stomach is obtained with doses of secretin smaller than those inducing a maximal response of the exocrine pancreas.