Recently, we described a novel preparation of rat stomach for vascular micropuncture studies. The aim of the present study was to directly measure basic microvascular parameters along the length of the gastric vasculature. Blood vessels were identified, and intravascular pressure was measured with a servo-null transducer, vessel dimensions with videometry, blood flow with microspheres, and plasma colloid osmotic pressure with an osmometer. When systemic arterial pressure was 100-110 mmHg, intravascular pressures in small arteries, primary, secondary, and tertiary submucosal arterioles, mucosal terminal arterioles, and muscle arterioles were 77.8 +/- 2.6, 74.6 +/- 2.5, 54.1 +/- 1.8, 34.4 +/- 1.6, 32.4 +/- 1.2, and 30.5 +/- 1.4 (SE) mmHg, respectively. Intravascular pressures in collecting veins, secondary and primary submucosal venules, muscle venules, and small veins were 26.6 +/- 1.1, 21.8 +/- 1.6, 17.1 +/- 0. 8, 18.2 +/- 0.9, and 14.4 +/- 0.6 mmHg, respectively. Capillary pressure in the mucosa (28 mmHg), as estimated by interpolation between terminal arteriole and collecting venule pressures, was significantly higher than in the muscle layer (23.6 +/- 1.4 mmHg). A total of 155 vessels from 25 animals were sampled. Relative blood flows were 16 +/- 3% in the muscle and 84 +/- 3% in the mucosa-submucosa. Analysis of filtration forces in these two different capillary beds suggests that gastric mucosal capillaries are primarily a filtering network, whereas muscle capillaries are in fluid balance. Calculated resistance ratios indicate low precapillary but relatively high postcapillary vascular resistance in the gastric mucosa.