The secretory response of the exocrine pancreas to an intravenous bolus of secretin (1.0 U/kg) was studied in healthy men and women below and above 45 years of age. We studied the secretory pattern, i.e., electrolyte and enzyme secretion in 8 sequential, 10-min collections and cumulative values for each parameter. Within the male group, no significant changes were observed, except for higher amylase and lipase secretions in the older subjects. On the other hand, females over 45 yr old had secretory patterns that showed a decline of flow and of bicarbonate concentration and output. No significant secretory differences were observed in the groups of younger males and females. When the over-45 groups of men and women were compared, the women exhibited a significant decrease in bicarbonate concentration and output. Moreover, this group of women had a cumulative 80-min output of bicarbonate and lipase significantly below these parameters in the men. Possible mechanisms are discussed.