Twelve horses, with acute laminitis (primarily in the forefeet) at 12 hours after intragastric dosing with an aqueous extract of black walnut (Juglans nigra) heart-wood, were studied. The distribution of perfusion of blood to the foot and to outlined regions within the foot was quantified, using gamma scintigraphy of regionally infused 99mTc-labeled macroaggregated albumin, before and 12 hours after extract administration. Horses 1 to 3 were not studied further. Perfusion was quantified again for horses 4 to 12 at 84 hours after extract administration. At the onset of acute laminitis, horses 7 to 12 were administered a single dose of prazosin (0.025 mg/kg of body weight, IV) immediately after scintigraphy of the right forelimb and before scintigraphy of the left forelimb. When compared with baseline images, perfusion to the forefoot of horses after the development of acute laminitis was quantitatively decreased vs perfusion to the entire distal portion of the forelimb. Also with the onset of laminitis, perfusion also decreased to the dorsal laminar and coronary corium regions vs the distal portion of the forelimb. The acute laminitis-associated deficit in perfusion to the dorsal laminitis-associated deficit in perfusion deficit in perfusion to either the coronary corium or the entire forefoot. Equivalent deficits in the distribution of perfusion were not detected in forelimbs from horses with acute laminitis and which had been treated with prazosin. When compared with baseline images, perfusion to the dorsal lamina was increased in relation to perfusion to the distal portion of the limb at postdosing hour 84. Prazosin treatment did not influence that increase in perfusion to the dorsal lamina.