The exocrine secretory function of the ventral and dorsal areas of the rat pancreas was investigated separately. In the isolated perfused rat pancreas, caerulein (10(-12), 10(-11), and 10(-10) M) and carbachol (10(-7) and 10(-6) M) caused a greaterfold increase in pancreatic secretion from the dorsal than the ventral area. Caerulein (10(-9) M) and carbachol (10(-5) M) were supramaximal concentrations with respect to secretion from the dorsal area, but this was not the case in the ventral area. Similar findings were also observed when ventral and dorsal secretions were studied in vivo in anesthetized animals. By contrast, in dispersed acini the sensitivity and responsiveness of tissue from the dorsal and ventral areas were similar to both secretagogues. The possible influence of the endocrine pancreas via the insuloacinar portal system was studied in the perfused pancreas of diabetic rats treated with insulin in vivo. Carbachol (10(-6) M)-stimulated secretion from the ventral area was similar (except for amylase) to that of controls, while a significantly reduced (P less than 0.001) output was measured from the dorsal pancreas. These results demonstrate that in the intact pancreas differences of exocrine secretion exist between the ventral and dorsal areas and suggest that insulin may contribute, at least in part, to the expression of such differences.