Gastric secretion was evaluated in 821 male inpatients aged 18-55 years with unaffected gastrointestinal, nervous and endocrine systems. With age, there was a tendency to increasing manufacture of gastric juice, hydrochloric acid, pepsin and gastric mucoprotein in 70% of the examinees. Reaching its maximum at the age of 25, the secretion remained stable for the following 15 years, progressively reducing thereafter. To the age of 50 gastric secretion diminished by 16.7%, the parameters lowing in the following order: volume of secretion, concentrations of hydrochloric acid, pepsin, gastric mucoprotein From the onset of physiological involution of the gastric glands observed usually at the age of 40 the response of the glands to reflex intestinal stimuli fell (explanation for basal secretion reduction), while that to humoral stimuli rose (cabbage-water). Hyposecretion may be, however, observed early in adolescence (10% of the examinees) and hypersecretion in middle life (20% of the examinees over 50). The results are thought helpful in clinical practice, occupational selection and mass health examinations of the population.