1. Glucagon (0-05 or 0-5 microng/kg. min) was infused into a mesenteric artery of a canine ileal segment from which transport was measured (direct infusion) or into a mesenteric artery of an adjacent non-perfused segment (indirect infusion). Unidirectional Na and H2O fluxes and arterial and mesenteric vein pressures and total and absorptive site blood flows were measured. 2. Direct glucagon infusion increased the absorptive and secretory fluxes of Na and H2O and absorptive site blood flow, and decreased absorptive site resistance and arterial and mesenteric vein pressure. Indirect glucagon infusion had the opposite effects. 3. Neither the direct arterial infusion of histamine (0-1-53 microng/kg. min) nor the I.V. infusion of glucose (0-2 g/min) or insulin (0-1 micron/kg) or glucose plus insulin, mimicked the effects of glucagon. 4. The unidirectional secretory and absorptive fluxes of both Na and H2O were linearly related to the calculated capillary pressure during glucagon infusion. 5. It was concluded that the effects of glucagon on gut transport were due to effects exerted through the cardiovascular system.