Roentgenograms of iothalamate meglumine 60% (Conray) injected bilaterally into the intercostal grooves of the 9th or 10th ribs in 30 surgical patients showed extensive spread of the contrast centrad and peripherally from the site of injection within 30 s, with almost complete absorption within 10 min 30 s. The spread was visualized in 2 patients for diagnosis using CT (computed tomography) following injection of iothalamate. It was confirmed by injecting liquid latex into 2 corpses prior to autopsy. These findings help to explain why the peak plasma level occurs more rapidly and is higher following intercostal nerve block than from other regional nerve blocks when comparable doses are injected. The study revealed that the optimal site for blocking an intercostal nerve is at the angle of the rib and that the optimal needle is one with a short bevel.