The capillary exchange capacity of the isolated, perfused dog stomach was investigated during vasoconstriction (norepinephrine) and vasodilation (isoproterenol) and compared with values obtained when blood flow to the stomach was decreased or increased mechanically. The capillary filtration coefficient (Kf,c) was used as an index of capillary exchange capacity. Under resting conditions, Kf,c in the isolated stomach was 0.20 +/- 0.02 ml . min-1 . mmHg-1 . 100 g-1. Vasoconstriction and mechanical reduction in blood flow caused Kf,c to fall to 68 and 58% of control, while vasodilation and mechanical increase in blood flow caused Kf,c to rise to 176 and 231% of control, respectively. Pentagastrin produced an increase in gastric oxygen consumption and a 50% increase in Kf,c. In all instances, capillary exchange capacity appeared to be correlated with gastric blood flow. The data suggest there is little local control of precapillary sphincter tone in the stomach and that capillary exchange capacity may be governed by local pressure within the microvasculature.