Abstract: Low activity heparin (38 U/kg, USP ⅩⅩ) 50 mg/kg given intravenously to rabbits reduced the uptake of ¹²⁵I-CH by the aorta wall. The inhibition rate was 530%. It was also found to inhibit the uptake of ¹²⁵I-CH by the aorta wall which was damaged by prior injection of noradrenaline. The inhibition rate was 34.6%. Twelve hours after injection of ¹²⁵I-CH 50 μCi/kg intravenously, the radioactivity in blood was not significantly different between the heparin treated and control groups, but ratio of radioactivity of the aorta wall and blood was significantly different. The effect of beparin on the endothelium permeability after a single intravenous injection lasted more than 24h.