Capsules (8 x 30 mm) of technetium-99m pertechnetate were designed for measurement of portal blood flow. Most of the radionuclide entered the superior mesenteric vein. The capsule was taken orally and monitored with a collimator for scintigraphy until it reached the small intestine, when a magnetic field completed an electrical circuit in a sensor, burning a thread, releasing a spring, and discharging the preparation. A study in crab-eating monkeys (Macaca fascicularis) showed that the radionuclide in the small intestine circulated through the superior mesenteric vein to the portal vein and liver. Portal scintigraphy through the small intestine could be analysed in the same way as per-rectal portal scintigraphy, in which blood flow mostly from the inferior mesenteric vein is evaluated. A study of four volunteers showed that, after the radionuclide was released, it circulated through the superior mesenteric vein to the portal vein and liver. Use of a capsule enclosing a radioisotope was possible, and the procedure seemed to be safe. The use of the per-small intestine method plus the per-rectal method should give more accurate results than either method used alone, because the haemodynamics of both the superior and inferior mesenteric vein would be reflected.